Fix KeyError being thrown when passing a mudata object to pl.clonotype_imbalance()

[frieseneggerf]

When passing a mudata object to pl.clonotype_imbalance() a "KeyError: '{key_added}'" is thrown.
Making sure adata is only accessed through the datahandler fixes this.

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

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 19.30%. Comparing base (6abf5ba) to head (3cd2515).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
src/scirpy/pl/_clonotype_imbalance.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #657       +/-   ##
===========================================
- Coverage   79.26%   19.30%   -59.96%     
===========================================
  Files          51       51               
  Lines        4576     4604       +28     
===========================================
- Hits         3627      889     -2738     
- Misses        949     3715     +2766     

Files with missing lines	Coverage Δ
src/scirpy/pl/_clonotype_imbalance.py	20.40% <0.00%> (-22.45%)	⬇️

... and 43 files with indirect coverage changes

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