Bug 481919

SUMMARY
***
NOTE: If you are reporting a crash, please try to attach a backtrace with debug symbols.
See https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports
***


STEPS TO REPRODUCE
1. Open a project with multiple timelines in RC
2. Do some editing in one timeline, save as new file.
3. Open in latest stable.

OBSERVED RESULT
I got a bunch of these messages 
```
Errors found when opening project file (Tue Feb 27 14:13:23 2024)
A1 00:00:56:10 Timeline clip (chain7) without bin reference found and removed.
A1 00:01:02:06 Timeline clip (chain7) without bin reference found and removed.
A1 00:01:14:19 Timeline clip (chain7) without bin reference found and removed.
A1 00:01:21:24 Timeline clip (chain7) without bin reference found and removed.
A1 00:01:33:07 Timeline clip (chain7) without bin reference found and removed.
A1 00:01:39:18 Timeline clip (chain128) without bin reference found and removed.
A1 00:01:48:15 Timeline clip (chain130) without bin reference found and removed.
A1 00:02:01:14 Timeline clip (chain130) without bin reference found and removed.
A1 00:02:38:08 Timeline clip (chain132) without bin reference found and removed.
A1 00:03:05:06 Timeline clip (chain132) without bin reference found and removed.
A1 00:03:16:18 Timeline clip (chain132) without bin reference found and removed.
A1 00:05:06:06 Timeline clip (chain4) without bin reference found and removed.
V1 00:00:56:10 Timeline clip (chain139) without bin reference found and removed.
V1 00:01:02:06 Timeline clip (chain139) without bin reference found and removed.
V1 00:01:14:19 Timeline clip (chain139) without bin reference found and removed.
V1 00:01:21:24 Timeline clip (chain139) without bin reference found and removed.
V1 00:01:33:07 Timeline clip (chain139) without bin reference found and removed.
V1 00:01:39:18 Timeline clip (chain140) without bin reference found and removed.
V1 00:01:48:15 Timeline clip (chain142) without bin reference found and removed.
V1 00:02:01:14 Timeline clip (chain142) without bin reference found and removed.
V1 00:02:38:08 Timeline clip (chain144) without bin reference found and removed.
V1 00:03:05:06 Timeline clip (chain144) without bin reference found and removed.
V1 00:03:16:18 Timeline clip (chain144) without bin reference found and removed.
V1 00:05:06:06 Timeline clip (chain6) without bin reference found and removed.
A4 00:00:15:00 Invalid clip (chain8) found and removed
A2 00:00:20:17 Timeline clip (producer5) without bin reference found and removed.
A2 00:00:38:14 Timeline clip (producer7) without bin reference found and removed.
A2 00:00:59:16 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:00:18 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:01:21 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:02:14 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:03:08 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:05:11 Timeline clip (chain12) without bin reference found and removed.
A2 00:01:06:07 Timeline clip (chain12) without bin reference found and removed.
A2 00:02:41:08 Timeline clip (chain14) without bin reference found and removed.
A1 00:00:15:00 Timeline clip (producer10) without bin reference found and removed.
A1 00:00:17:06 Timeline clip (producer11) without bin reference found and removed.
A1 00:00:18:14 Timeline clip (producer12) without bin reference found and removed.
A1 00:00:19:18 Timeline clip (producer13) without bin reference found and removed.
A1 00:00:39:10 Timeline clip (chain16) without bin reference found and removed.
A1 00:00:55:23 Timeline clip (chain18) without bin reference found and removed.
A1 00:00:57:19 Timeline clip (producer22) without bin reference found and removed.
A1 00:01:04:04 Timeline clip (chain18) without bin reference found and removed.
A1 00:01:05:02 Timeline clip (chain18) without bin reference found and removed.
V1 00:00:15:00 Timeline clip (producer41) without bin reference found and removed.
V1 00:00:17:06 Timeline clip (producer42) without bin reference found and removed.
V1 00:00:18:14 Timeline clip (producer43) without bin reference found and removed.
V1 00:00:19:18 Timeline clip (producer44) without bin reference found and removed.
V1 00:00:39:10 Timeline clip (chain24) without bin reference found and removed.
V1 00:00:55:23 Timeline clip (chain26) without bin reference found and removed.
V1 00:00:57:19 Timeline clip (producer53) without bin reference found and removed.
V1 00:01:04:04 Timeline clip (chain26) without bin reference found and removed.
V1 00:01:05:02 Timeline clip (chain26) without bin reference found and removed.
V2 00:00:20:17 Timeline clip (producer72) without bin reference found and removed.
V2 00:00:38:14 Timeline clip (producer74) without bin reference found and removed.
V2 00:00:59:16 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:00:18 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:01:21 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:02:14 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:03:08 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:05:11 Timeline clip (chain176) without bin reference found and removed.
V2 00:01:06:07 Timeline clip (chain176) without bin reference found and removed.
```

It is noticeable these only happened in the Assembly and Rough Cut timelines, not in the Fine cut timeline I had been making changes in.

EXPECTED RESULT
Probably something like this since opening a new project file version in an old version is bound to cause some problems.


SOFTWARE/OS VERSIONS
Operating System: NixOS 23.11
KDE Plasma Version: 5.27.10
KDE Frameworks Version: 5.113.0
Qt Version: 5.15.12
Kernel Version: 6.1.76-xanmod1 (64-bit)
Graphics Platform: X11
Processors: 8 × AMD Ryzen Embedded V1605B with Radeon Vega Gfx
Memory: 14.6 GiB of RAM
Graphics Processor: AMD Ryzen Embedded V1605B with Radeon Vega Gfx

ADDITIONAL INFORMATION