Tests: Update the URL to the documentation on GitHub Actions environment variables.

Follow-up to [49264].

See #55652.

git-svn-id: https://develop.svn.wordpress.org/trunk@53467 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/abstract-testcase.php

@@ -212,7 +212,7 @@ abstract class WP_UnitTestCase_Base extends PHPUnit_Adapter_TestCase {
 	 * we want to skip tests that only need to run for trunk.
 	 */
 	public function skipOnAutomatedBranches() {
-		// https://docs.github.com/en/free-pro-team@latest/actions/reference/environment-variables#default-environment-variables
+		// https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
 		$github_event_name = getenv( 'GITHUB_EVENT_NAME' );
 		$github_ref        = getenv( 'GITHUB_REF' );