Fix collection name validation

[kmike]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.38%. Comparing base (8927379) to head (ad6a58c).

Additional details and impacted files

@@                Coverage Diff                @@
##           articles_to_main     #100   +/-   ##
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  Coverage             95.38%   95.38%           
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  Files                    25       25           
  Lines                  2449     2449           
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  Hits                   2336     2336           
  Misses                  113      113           

Files with missing lines	Coverage Δ
zyte_spider_templates/spiders/article.py	85.62% <ø> (ø)

[kmike]

This doesn't enable UI validation for some reason (looks like a bug - is pattern validation supported for nullable string fields in the SC UI?), but at least it fails in a spider, and also adds a suggestion to the user not to use such collection names.

[kmike]

I can confirm that when the field is made required, validation starts to work.