Fixes for mudata 0.4

[grst]

Closes #...

• CHANGELOG.md updated
• Tests added (For bug fixes or new features)
• Tutorial updated (if necessary)

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[codecov]

Codecov Report

❌ Patch coverage is 41.66667% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.46%. Comparing base (efe49e6) to head (6afaaa6).

Files with missing lines	Patch %	Lines
src/scirpy/datasets/__init__.py	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #744      +/-   ##
==========================================
+ Coverage   78.32%   78.46%   +0.14%     
==========================================
  Files          51       51              
  Lines        4628     4635       +7     
==========================================
+ Hits         3625     3637      +12     
+ Misses       1003      998       -5     

Files with missing lines	Coverage Δ
src/scirpy/tests/conftest.py	100.00% <100.00%> (ø)
src/scirpy/tests/util.py	100.00% <100.00%> (ø)
src/scirpy/datasets/__init__.py	82.35% <12.50%> (-2.84%)	⬇️

... and 2 files with indirect coverage changes

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