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 63.63636% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.51%. Comparing base (5b1a8c5) to head (9af2a0b).

Files with missing lines	Patch %	Lines
src/anndata/_core/anndata.py	75.00%	2 Missing ⚠️
src/anndata/_core/raw.py	33.33%	2 Missing ⚠️

❌ Your project check has failed because the head coverage (47.51%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (5b1a8c5) and HEAD (9af2a0b). Click for more details.

HEAD has 11 uploads less than BASE

Flag	BASE (5b1a8c5)	HEAD (9af2a0b)
	12	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2351       +/-   ##
===========================================
- Coverage   87.34%   47.51%   -39.83%     
===========================================
  Files          49       49               
  Lines        7775     7780        +5     
===========================================
- Hits         6791     3697     -3094     
- Misses        984     4083     +3099     

Files with missing lines	Coverage Δ
src/anndata/_core/anndata.py	49.33% <75.00%> (-34.00%)	⬇️
src/anndata/_core/raw.py	45.51% <33.33%> (-34.07%)	⬇️

... and 32 files with indirect coverage changes