Bug 450484

SUMMARY
If I open a .R file with Kate, it will show the operator ":=" with an extra underline in the right sign, making it show **three** bars instead of two. This is very annoying since it makes it harder to read the code and makes people think they've inputted the wrong symbol. These two symbols together (:=) are very common in R code, and what's more, kate's coloring backed is offered as one of the styles for "rmarkdown" (what most people use to write tutorials, manuals, vignettes, etc. with R code), but this issue makes it a very unsuitable candidate (and it's understandably not the default BTW, even though it otherwise looks better than the default style from rmarkdown). I have on multiple ocassions decided to use a Python syntax highlighter for R code instead due to this issue alone.

STEPS TO REPRODUCE
1. Save this text as a .R file and open it with Kate:
library(data.table)
dt <- data.table(col1 = 1:3)
dt[, col1 := col1+1]

OBSERVED RESULT
The ":=" operator has three lines.

EXPECTED RESULT
The ":=" operator should have two lines.

SOFTWARE/OS VERSIONS
Operating System: Debian GNU/Linux
KDE Plasma Version: 5.23.5
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.2
Kernel Version: 5.15.0-2-amd64 (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 2700 Eight-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: AMD VEGA10