fix: Don't use deprecated logger.warn

[sentrivana]

logger.warn() is deprecated in favor of logger.warning().

We were using logger.warn() in two places. I changed one to debug to not pollute folks' logs and the other one to logger.warning() since it's in the tests.

[szokeasaurusrex]

nice

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.51%. Comparing base (64e2977) to head (f796ddc).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/langchain.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3552      +/-   ##
==========================================
- Coverage   84.51%   84.51%   -0.01%     
==========================================
  Files         133      133              
  Lines       13837    13837              
  Branches     2927     2927              
==========================================
- Hits        11695    11694       -1     
  Misses       1415     1415              
- Partials      727      728       +1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/langchain.py	69.87% <0.00%> (ø)

... and 1 file with indirect coverage changes