ci: Increase max_locks_per_transaction for Python tests

[khvn26]

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Changes

In this PR, we attempt to fix the django.db.utils.OperationalError: out of shared memory error in CI by increasing default max_locks_per_transaction for the test databases. As a side effect, we move from Postgres services defined in Github Actions to a more centralised Compose-based approach.

How did you test this code?

This is a CI change.

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3 Skipped Deployments

Project	Deployment	Review	Updated (UTC)
docs	Ignored	Preview	Jan 21, 2026 10:42am
flagsmith-frontend-preview	Ignored	Preview	Jan 21, 2026 10:42am
flagsmith-frontend-staging	Ignored	Preview	Jan 21, 2026 10:42am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-6569	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-6569	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-6569	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-6569	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-6569	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6569	Finished ✅	Results ✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.15%. Comparing base (2cb22c4) to head (c0a9844).
⚠️ Report is 1 commits behind head on ci/private-packages-test-improvements.

Additional details and impacted files

@@                          Coverage Diff                           @@
##           ci/private-packages-test-improvements    #6569   +/-   ##
======================================================================
  Coverage                                  98.15%   98.15%           
======================================================================
  Files                                       1293     1293           
  Lines                                      46610    46610           
======================================================================
  Hits                                       45751    45751           
  Misses                                       859      859           

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