Calculate junction_aa in IEDB

[grst]

Closes #469

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

[codecov]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (759bc44) 80.50% compared to head (7a2f140) 80.22%.

Files	Patch %	Lines
src/scirpy/datasets/__init__.py	4.76%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #476      +/-   ##
==========================================
- Coverage   80.50%   80.22%   -0.28%     
==========================================
  Files          49       49              
  Lines        4000     4015      +15     
==========================================
+ Hits         3220     3221       +1     
- Misses        780      794      +14     

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[grst]

This needs another solution as the protein sequence is missing too often.