Address some typing errors

[fepegar]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 84.49%. Comparing base (6596899) to head (8517542).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/torchio/data/image.py	0.00%	2 Missing ⚠️
src/torchio/data/io.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1253      +/-   ##
==========================================
- Coverage   87.13%   84.49%   -2.64%     
==========================================
  Files          92       92              
  Lines        5962     5966       +4     
==========================================
- Hits         5195     5041     -154     
- Misses        767      925     +158     

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