feat(github): add immutable releases check

[Sakeeb91]

Closes #9084

Summary

• add repository_immutable_releases_enabled GitHub repository check that reports PASS/FAIL when immutable releases are enforced
• extend the repository service to call the /repos/{owner}/{repo}/immutability REST endpoint using existing auth and expose the result on the repository model
• include descriptive metadata (high severity, remediation guidance) and align the check folder layout with other GitHub repository checks

Implementation Details

• introduced _get_repository_immutable_releases_status to retrieve the immutability flag, handling 404 (not available) and 403 (insufficient permissions) responses without failing the scan
• normalized preview API responses via _normalize_immutability_value and _parse_immutability_response, covering both boolean and string states as well as nested payloads
• updated repository service fixtures plus added PASS/FAIL/unknown tests for the new check to ensure coverage of each outcome

Testing

• poetry run pytest tests/providers/github/services/repository

[github-actions]

✅ Conflict Markers Resolved

All conflict markers have been successfully resolved in this pull request.

[andoniaf]

Thanks @Sakeeb91 for the contribution! I'll take a look to this next week 👍

[andoniaf]

While testing I found an issue. I misswrote the endpoint for the inmutability in the issue description, is not GET /repos/{owner}/{repo}/immutability it is /repos/{owner}/{repo}/immutable-releases.

I took care of it, and now it's working fine:

[codecov]

Codecov Report

❌ Patch coverage is 69.44444% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.02%. Comparing base (6e135ab) to head (53245a6).
⚠️ Report is 4 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (6e135ab) and HEAD (53245a6). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (6e135ab)	HEAD (53245a6)
api	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #9162       +/-   ##
===========================================
- Coverage   92.58%   78.02%   -14.56%     
===========================================
  Files         154       30      -124     
  Lines       21271     1065    -20206     
===========================================
- Hits        19693      831    -18862     
+ Misses       1578      234     -1344     

Flag	Coverage Δ
api	?
prowler-py3.10-github	78.02% <69.44%> (?)
prowler-py3.11-github	78.02% <69.44%> (?)
prowler-py3.12-github	78.02% <69.44%> (?)
prowler-py3.9-github	78.02% <69.44%> (?)

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Components	Coverage Δ
prowler	78.02% <69.44%> (∅)
api	∅ <ø> (∅)

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