Fix class variable not being used for vdims in RGB

[hoxbro]

No description provided.

[codecov-commenter]

Codecov Report

Merging #5773 (beef385) into main (68e87da) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5773   +/-   ##
=======================================
  Coverage   88.17%   88.17%           
=======================================
  Files         306      306           
  Lines       62767    62772    +5     
=======================================
+ Hits        55346    55351    +5     
  Misses       7421     7421           

Impacted Files	Coverage Δ
holoviews/element/raster.py	78.92% <100.00%> (ø)
holoviews/tests/element/test_raster.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[maximlt]

Ush that was a tricky one to hunt!

I'd be great if you could write up what you fixed/was wrong in the body of the PR. I'm just way too sad when I end up on such a PR in a git blame session.

[hoxbro]

I'd be great if you could write up what you fixed/was wrong in the body of the PR. I'm just way too sad when I end up on such a PR in a git blame session.

My idea was to explain it in the comment + having a test for it. I will add a small description in the new PR.

I know this was pretty lazy of me, but I wanted it merged so I could continue to work on another issue (#5774).