Build/Test Tools: Prevent PHPUnit tests on push for forks/private mirrors.

The reorganization of the PHPUnit workflow in [50441] unintentionally caused the tests to be run for every `push` event, even for forks and private mirrors.

Previously, the second job required the first one to pass, and the conditional check on the first prevented both from running. Because the first job is no longer required for the second, both jobs must have the appropriate conditional check.

Merges [50670] to the 5.6 branch.
Fixes #52983.

git-svn-id: https://develop.svn.wordpress.org/branches/5.6@50672 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/phpunit-tests.yml

@@ -70,6 +70,7 @@ jobs:
   test-php:
     name: ${{ matrix.php }}${{ matrix.multisite && ' multisite' || '' }}${{ matrix.split_slow && ' slow tests' || '' }} ${{ matrix.memcached && ' with memcached' || '' }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
+    if: ${{ github.repository == 'WordPress/wordpress-develop' || github.event_name == 'pull_request' }}
     strategy:
       fail-fast: false
       matrix: