Enable doctests

[tsalo]

Closes #1408.

Changes proposed in this pull request

• Enable doctests in unit test CircleCI job.
• Fix doctests that are failing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.07%. Comparing base (3321d2f) to head (6f65dbe).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1410   +/-   ##
=======================================
  Coverage   79.06%   79.07%           
=======================================
  Files          58       58           
  Lines        7347     7349    +2     
  Branches      970      970           
=======================================
+ Hits         5809     5811    +2     
  Misses       1256     1256           
  Partials      282      282           

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[tsalo]

Enabling the doctests causes the following unit tests to fail:

FAILED xcp_d/tests/test_utils_bids.py::test_collect_participants - Failed: DID NOT WARN. No warnings of type (<class 'xcp_d.utils.bids.BIDSWarning'>,) were emitted.
 Emitted warnings: [].
FAILED xcp_d/tests/test_utils_confounds.py::test_modify_motion_filter - Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) were emitted.
 Emitted warnings: [].

These are the only tests that use pytest.warns, so I think the doctests must be filtering out warnings.