FIX: Don't crash on non-string BIDS filter values

[lobennett]

Closes #3394.

Changes proposed in this pull request

• Replace not isinstance(value, Query) with isinstance(value, str) in _process_value (fmriprep/config.py, called during --bids-filter-file unserialization).

Why

_process_value was checking 'Query' in value for any non-Query input, which raised TypeError: argument of type 'int' is not iterable whenever a filter value was an int or float (e.g. {"inv": 2} in the JSON filter file). Using isinstance(value, str) as the guard skips the substring check for non-string scalars, so they pass through unchanged.

The Query-passthrough behavior previously provided by not isinstance(value, Query) is preserved naturally: Query enum members are not instances of str, so the guard short-circuits and the value is returned unchanged.

Testing

• Verified the fixed conditional locally against int, float, bool, plain strings, lists with mixed scalar types, repr(Query.OPTIONAL) (the existing Query-repr unserialize path), and existing Query instances. All pass through or unserialize as expected.
• ruff check, ruff format --check, and codespell pass on the modified file.

Documentation that should be reviewed

None.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.57%. Comparing base (acdb0fd) to head (64ee747).
⚠️ Report is 12 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3641   +/-   ##
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  Coverage   74.57%   74.57%           
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  Files          62       62           
  Lines        4975     4975           
  Branches      637      637           
=======================================
  Hits         3710     3710           
  Misses       1131     1131           
  Partials      134      134           

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