[FIX] find confounds even when BIDS derivatives bold files contain res or den entities

[Remi-Gau]

Fixes #3741

Changes proposed in this pull request:

• make test for first_level_from_bids more stringent by checking the types of the output values
• fix bug by not allowing any derivative entities when filtering for confounds

[github-actions]

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[codecov]

Codecov Report

Merging #3742 (e1b0376) into main (4493330) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3742      +/-   ##
==========================================
- Coverage   91.60%   91.54%   -0.07%     
==========================================
  Files         139      139              
  Lines       16593    16591       -2     
  Branches     3244     3244              
==========================================
- Hits        15200    15188      -12     
- Misses       1390     1402      +12     
+ Partials        3        1       -2     

Impacted Files	Coverage Δ
nilearn/glm/first_level/first_level.py	96.78% <ø> (-0.02%)	⬇️
nilearn/_utils/data_gen.py	98.43% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[bthirion]

LGTM, thx

[ymzayek]

LGTM! Minor comments

[Remi-Gau]

all green

merging