Bug 503908

SUMMARY
When attempting to add a DAV groupware resource calendar source, the credential window asking for a username and a password appears briefly, but closes itself about one second later. This makes it impossible to add a CalDAV calendar to Merkuro.

STEPS TO REPRODUCE
1. Set up an Arch Linux system with KDE Plasma. Install Merkuro. Open the application.
2. Go to Settings → Configure Merkuro Calendar... → Accounts → Add Account
3. Chose "DAV groupware resource"
4. Observe the credential window opening and closing.

OBSERVED RESULT
The credential window closes itself after about one second.
It does not appear to be a crash. Merkuro stays functional.

EXPECTED RESULT
The credential window should stay open, allowing the user to enter credentials.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.13.0
Qt Version: 6.9.0
Kernel Version: 6.14.5-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 3900X 12-Core Processor
Memory: 62.7 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 2080 Ti

ADDITIONAL INFORMATION
I checked dmesg and the "Crashed Process Viewer" to confirm that there is no crash occuring.
Also, shouldn't the credential window ask for a URL as well?

LOG OUTPUT
I ran Merkuro from a terminal and reproduced the bug. The log output seems unrelated:
```
qrc:/qt/qml/org/kde/merkuro/calendar/qml/Main.qml:683:9: QML ScheduleView: Created graphical object was not placed in the graphics scene.
qrc:/qt/qml/org/kde/merkuro/calendar/qml/Main.qml:659:9: QML MonthView: Created graphical object was not placed in the graphics scene.
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
qrc:/qt/qml/org/kde/kirigamiaddons/statefulapp/labs/NativeMenuItem.qml:55: ReferenceError: parent is not defined
kf.i18n: 0 instead of 1 arguments to message "Configure %1" supplied before conversion
qrc:/qt/qml/org/kde/akonadi/AgentConfigurationForm.qml:113:9: QML ScrollablePage: Created graphical object was not placed in the graphics scene.
```