feat: clean-site-packages-before-mv

[Zaimwa9]

Thanks for submitting a PR! Please check the boxes below:

• I have read the Contributing Guide.
• I have added information to docs/ if required so people know about the feature.
• I have filled in the "Changes" section below.
• I have filled in the "How did you test this code" section below.

Changes

API tests are failing due to poetry cache during CI cf here

• Cleans-up the site packages before trying to install them

How did you test this code?

• CI

[vercel]

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3 Skipped Deployments

Project	Deployment	Review	Updated (UTC)
docs	Ignored		Jan 21, 2026 9:29am
flagsmith-frontend-preview	Ignored		Jan 21, 2026 9:29am
flagsmith-frontend-staging	Ignored		Jan 21, 2026 9:29am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-6568	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-6568	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api-test:pr-6568	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-6568	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-6568	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6568	Finished ✅	Results ✅

[matthewelwell]

Duplicate of #6566

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.15%. Comparing base (217f217) to head (83bb10b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6568   +/-   ##
=======================================
  Coverage   98.15%   98.15%           
=======================================
  Files        1293     1293           
  Lines       46610    46610           
=======================================
  Hits        45751    45751           
  Misses        859      859           

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