fix: check .raw length on setting

[flying-sheep]

• Closes adata.obs_names should be the same as adata.raw.obs_names #449
• Tests added
• Release note added (or unnecessary)

Going through all the newly marked as stale issues, and while a lot can be closed, some are still valid!

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.35%. Comparing base (c67c66d) to head (e9ee761).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/anndata/_core/anndata.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2351      +/-   ##
==========================================
+ Coverage   87.34%   87.35%   +0.01%     
==========================================
  Files          49       49              
  Lines        7775     7784       +9     
==========================================
+ Hits         6791     6800       +9     
  Misses        984      984              

Files with missing lines	Coverage Δ
src/anndata/_core/raw.py	80.66% <100.00%> (+1.08%)	⬆️
src/anndata/_core/anndata.py	83.35% <88.88%> (+0.02%)	⬆️