FIX: Plot carpetplot with CIFTI-specific colorbar

[oesteban]

The final integration of the edge mask had missed that detail. It went undetected as the reports on Circle did not show CIFTI outputs. Now that is resolved and this PR should conclude the carpet refactor.

Changes proposed in this pull request

Documentation that should be reviewed

[codecov-commenter]

Codecov Report

Merging #2737 (9e6c2d5) into master (b6f8dbd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2737   +/-   ##
=======================================
  Coverage   46.10%   46.10%           
=======================================
  Files          44       44           
  Lines        3325     3325           
=======================================
  Hits         1533     1533           
  Misses       1792     1792           

Impacted Files	Coverage Δ
fmriprep/interfaces/confounds.py	64.19% <ø> (ø)

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