Fix CI: suppress RepeatedField psalm errors, restore PHP 8.1 support

[bobstrecansky]

Summary

• Add Psalm UndefinedDocblockClass suppression for Google\Protobuf\Internal\RepeatedField (mirrors the existing UndefinedMethod suppression for the same class). Clears the 32 errors blocking PHP QA on 8.2 / 8.3 / 8.4.
• Revert two renovate bumps that together broke composer install on PHP 8.1: pin phpspec/prophecy back to 1.22.* (1.23+ dropped PHP 8.1) and phpdocumentor/reflection-docblock back to ^5.3 (prophecy 1.22 conflicts with v6). Restores the project's declared "php": "^8.1" support.

Supersedes #1959 (same psalm fix) and reverts the install-breaking parts of #1915 and #1919.

Test plan

• PHP QA workflow goes green on 8.1 / 8.2 / 8.3 / 8.4
  EOF

[linux-foundation-easycla]

• ✅ login: bobstrecansky / name: bobstrecansky (eb9ec6c)
• ❌ The email address for the commit (eb9ec6c) is not linked to the GitHub account, preventing the EasyCLA check. Consult this Help Article and GitHub Help to resolve. (To view the commit's email address, add .patch at the end of this PR page's URL.) For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

One or more co-authors of this pull request were not found. You must specify co-authors in commit message trailer via:

Co-authored-by: name <email>

Supported Co-authored-by: formats include:

1. Anything <id+login@users.noreply.github.com> - it will locate your GitHub user by id part.
2. Anything <login@users.noreply.github.com> - it will locate your GitHub user by login part.
3. Anything <public-email> - it will locate your GitHub user by public-email part. Note that this email must be made public on Github.
4. Anything <other-email> - it will locate your GitHub user by other-email part but only if that email was used before for any other CLA as a main commit author.
5. login <any-valid-email> - it will locate your GitHub user by login part, note that login part must be at least 3 characters long.

Alternatively, if the co-author should not be included, remove the Co-authored-by: line from the commit message.

Please update your commit message(s) by doing git commit --amend and then git push [--force] and then request re-running CLA check via commenting on this pull request:

/easycla

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.85%. Comparing base (471b51d) to head (eb9ec6c).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1965      +/-   ##
============================================
+ Coverage     67.75%   67.85%   +0.09%     
  Complexity     3044     3044              
============================================
  Files           459      459              
  Lines          8883     8885       +2     
============================================
+ Hits           6019     6029      +10     
+ Misses         2864     2856       -8     

Flag	Coverage Δ
8.1	67.63% <ø> (?)
8.5	67.72% <ø> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 7 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 471b51d...eb9ec6c. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.