fix(hybrid-cloud): Sets region mode to default test, unless monolith dbs specified

[GabeVillalobos]

Sets region mode on all testing by default unless SENTRY_USE_MONOLITH_DBS option is set. This allows import/export tests to complete their testing as expected.

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e88984d) 81.40% compared to head (ba60ec6) 81.39%. Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #65021      +/-   ##
==========================================
- Coverage   81.40%   81.39%   -0.01%     
==========================================
  Files        5251     5251              
  Lines      232127   232183      +56     
  Branches    45575    45592      +17     
==========================================
+ Hits       188963   188991      +28     
- Misses      37278    37301      +23     
- Partials     5886     5891       +5     

Files	Coverage Δ
src/sentry/testutils/pytest/sentry.py	84.13% <100.00%> (+0.07%)	:arrow_up:
...y/api/endpoints/group_similar_issues_embeddings.py	95.12% <80.00%> (+0.12%)	:arrow_up:

... and 19 files with indirect coverage changes