detect-filename: convert unittests to FAIL/PASS APIs

[AkakiAlice]

Task: #4036

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• I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• I have signed the Open Information Security Foundation contribution agreement at https://suricata.io/about/contribution-agreement/
• I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket: https://redmine.openinfosecfoundation.org/issues/4036

Describe changes:

• Update detect-filename unit tests to use FAIL/PASS APIs.

[codecov]

Codecov Report

Merging #8036 (f56ea5e) into master (2158dbf) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8036      +/-   ##
==========================================
- Coverage   81.65%   81.63%   -0.02%     
==========================================
  Files         953      953              
  Lines      275749   275744       -5     
==========================================
- Hits       225158   225112      -46     
- Misses      50591    50632      +41     

Flag	Coverage Δ
fuzzcorpus	63.70% <ø> (+0.31%)	⬆️
suricata-verify	58.89% <ø> (-0.04%)	⬇️
unittests	63.47% <100.00%> (+<0.01%)	⬆️

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[jufajardini]

Looks good to me, thanks! :)

[victorjulien]

Merged in #8085, thanks!