Fix #416: Fix undesired assignment to "pretrained" in test.py

[gaotongxiao]

Some models no longer accept pretrained parameter in their constructors and use init_cfg to initialize themselves instead. But test.py still passes None to pretrained whichever the model is being tested. So I added a simple check to skip this step.

Also fixed a linting problem.

[codecov]

Codecov Report

Merging #418 (80a0437) into main (f62b451) will decrease coverage by 0.09%.
The diff coverage is n/a.

❗ Current head 80a0437 differs from pull request most recent head c38a4d9. Consider uploading reports for the commit c38a4d9 to get more accurate results

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   82.35%   82.25%   -0.10%     
==========================================
  Files         137      137              
  Lines        9260     9260              
  Branches     1322     1322              
==========================================
- Hits         7626     7617       -9     
- Misses       1336     1345       +9     
  Partials      298      298              

Flag	Coverage Δ
unittests	82.25% <ø> (-0.10%)	⬇️

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Impacted Files	Coverage Δ
mmocr/utils/ocr.py	0.00% <ø> (ø)
mmocr/models/textrecog/convertors/seg.py	91.78% <0.00%> (-2.74%)	⬇️
mmocr/datasets/pipelines/transforms.py	80.36% <0.00%> (-1.16%)	⬇️

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