fix(ci): merge release commits through prs

[hadrien]

Problem

• Protected main rejects direct release pushes after the exact SHA passes every required check.
• The ruleset reports those successful checks as expected during direct promotion.

Solution

• Open a conventional PR for each generated release commit.
• Dispatch and wait for CI on the PR head.
• Squash-merge through the protected-main API with a pinned SHA.
• Tag the resulting main commit before publishing.
• Preserve docs, GitHub release notes, and PyPI publication.
• Keep every main mutation inside the normal ruleset path.

fs-3z4

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.74%. Comparing base (5dd5369) to head (b9f5f8a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #132   +/-   ##
=======================================
  Coverage   97.74%   97.74%           
=======================================
  Files           1        1           
  Lines         133      133           
  Branches        7        7           
=======================================
  Hits          130      130           
  Misses          3        3           

Flag	Coverage Δ
fastapi-post121	97.74% <ø> (ø)
fastapi-pre121	97.74% <ø> (ø)
sqlmodel	97.74% <ø> (ø)

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