Fix groupby option for vectorized annotations

[Hoxbro]

No description provided.

[codecov-commenter]

Codecov Report

Merging #5956 (1d746aa) into main (bb81fe0) will decrease coverage by 0.01%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5956      +/-   ##
==========================================
- Coverage   88.58%   88.58%   -0.01%     
==========================================
  Files         315      315              
  Lines       65523    65516       -7     
==========================================
- Hits        58043    58036       -7     
  Misses       7480     7480              

Flag	Coverage Δ
ui-tests	23.14% <28.57%> (+<0.01%)	⬆️

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Files	Coverage Δ
holoviews/plotting/bokeh/__init__.py	98.14% <100.00%> (ø)
holoviews/plotting/bokeh/annotation.py	86.78% <100.00%> (+0.03%)	⬆️
...oviews/tests/plotting/bokeh/test_annotationplot.py	97.71% <100.00%> (-0.05%)	⬇️

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