Build/Test Tools: Stop committing changes to tracked files in pull requests.

This workflow has not proven to be as useful as originally hoped, so it's being removed to reduce maintenance burden. All workflows that run the build script already fail if they result in untracked changes.

Merges r63315 to the 6.9 branch.

See #65845.


git-svn-id: https://develop.svn.wordpress.org/branches/6.9@65297 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj