fix(celery): Latency should be in milliseconds, not seconds

[sentrivana]

Fixes #4636

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.61%. Comparing base (19ed1bb) to head (eb19c7d).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4637      +/-   ##
==========================================
- Coverage   80.65%   80.61%   -0.04%     
==========================================
  Files         156      156              
  Lines       16513    16514       +1     
  Branches     2806     2806              
==========================================
- Hits        13318    13313       -5     
- Misses       2307     2312       +5     
- Partials      888      889       +1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/celery/__init__.py	86.61% <100.00%> (+0.05%)	⬆️

... and 1 file with indirect coverage changes