Handle loguru msg levels that are not supported by Sentry

[antonpirker]

Loguru has two message levels TRACE and SUCCESS that are not available in Sentry breadcrumbs. This PR maps TRACE to debug and SUCCESS to info in Sentry so those breadcrumbs do not show a confusing error message in the Sentry UI.

Fixes #2759

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.50%. Comparing base (bc54a1d) to head (4601407).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/loguru.py	66.66%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4147      +/-   ##
==========================================
- Coverage   79.57%   79.50%   -0.08%     
==========================================
  Files         141      141              
  Lines       15714    15723       +9     
  Branches     2671     2673       +2     
==========================================
- Hits        12505    12501       -4     
- Misses       2367     2377      +10     
- Partials      842      845       +3     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/loguru.py	88.13% <66.66%> (-1.87%)	⬇️

... and 7 files with indirect coverage changes

[sentrivana]

Looks ok, but the tests need fixing.

[andyshinn]

Thanks for eventually getting to this! I know it's small but I always appreciate when I don't need to see weird warnings staring back at me in the UI.