Fix username validation in rws.

[veluca93]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.72%. Comparing base (1914a5a) to head (491ed4f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cmsranking/Store.py	0.00%	5 Missing ⚠️
cmsranking/RankingWebServer.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1728      +/-   ##
==========================================
- Coverage   56.72%   56.72%   -0.01%     
==========================================
  Files         344      344              
  Lines       28312    28314       +2     
==========================================
+ Hits        16060    16061       +1     
- Misses      12252    12253       +1     

Flag	Coverage Δ
functionaltests	0.00% <0.00%> (ø)
unittests	56.72% <0.00%> (-0.01%)	⬇️

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