Update legacy_anndata.py

[Liripo]

Convert to RGB format so that colors will display correctly as RGB in napari-spatialdata.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.06%. Comparing base (7c19850) to head (5aa46df).
⚠️ Report is 52 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #320       +/-   ##
===========================================
+ Coverage   38.75%   49.06%   +10.30%     
===========================================
  Files          26       26               
  Lines        2709     2686       -23     
===========================================
+ Hits         1050     1318      +268     
+ Misses       1659     1368      -291     

Files with missing lines	Coverage Δ
src/spatialdata_io/converters/legacy_anndata.py	51.77% <ø> (ø)

... and 6 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.