Update branches build status in README

[Francisco-Gamino]

Issue describing the changes in this PR

Update README with the following:

• Add build status for the v4.x/ps7.4 branch
• Remove build status for v2.x, v3.x/ps6, and v3.x/ps7 branches

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information