fix: stray commands

[Laerte]

This behaviour was introduced on: #4552

We created a new class that inherit from ScrapyCommand but forget to check on _iter_command_classes function, this is the reason that command was appearing loose.

Close: #5711, Fixes: #5709

[codecov]

Codecov Report

Merging #5712 (c6c60e6) into master (bbe24d7) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head c6c60e6 differs from pull request most recent head a55f8f7. Consider uploading reports for the commit a55f8f7 to get more accurate results

@@            Coverage Diff             @@
##           master    #5712      +/-   ##
==========================================
- Coverage   88.87%   88.85%   -0.02%     
==========================================
  Files         162      162              
  Lines       11026    11026              
  Branches     1808     1808              
==========================================
- Hits         9799     9797       -2     
- Misses        947      948       +1     
- Partials      280      281       +1     

Impacted Files	Coverage Δ
scrapy/cmdline.py	67.96% <100.00%> (ø)
scrapy/core/downloader/__init__.py	90.97% <0.00%> (-1.51%)	⬇️

[Gallaecio]

Great!