Fix fMRIPrep-related bugs

[tsalo]

Closes none, but addresses ASLPrep's copy of multiple 23.2.0a2-related fMRIPrep bugs.

Changes proposed in this pull request

• Fix CIFTI density bug (FIX: Retrieve atlas ROIs at requested density nipreps/fmriprep#3179)
• Ignore sbrefs when requested (FIX: Restore --ignore sbref functionality nipreps/fmriprep#3180)
  • Technically, sbrefs aren't supported for ASL data yet, so this won't change behavior.

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (67607e1) 78.81% compared to head (a80e021) 78.73%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
aslprep/workflows/asl/fit.py	44.44%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #366      +/-   ##
==========================================
- Coverage   78.81%   78.73%   -0.08%     
==========================================
  Files          39       39              
  Lines        4149     4158       +9     
  Branches      600      602       +2     
==========================================
+ Hits         3270     3274       +4     
- Misses        685      688       +3     
- Partials      194      196       +2     

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