Now printing to log.debug (vs warning) when a file name comprises multiple dots (closes #3899)

[nicolasrochette]

This PR is to address issue #3899

Minor, but thanks again

• Closes irrelevant warning in sc.readwrite.is_valid_filename #3899
• [Tests][] included or not required because: trivial change
• [Release notes][] not necessary because: too minor

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.73%. Comparing base (452c4f6) to head (ad7fca9).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/scanpy/readwrite.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #3924       +/-   ##
=========================================
+ Coverage      0   76.73%   +76.73%     
=========================================
  Files         0      116      +116     
  Lines         0    12403    +12403     
=========================================
+ Hits          0     9517     +9517     
- Misses        0     2886     +2886     

Flag	Coverage Δ
hatch-test.pre	76.73% <0.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/scanpy/readwrite.py	76.59% <0.00%> (ø)

... and 115 files with indirect coverage changes