Build/Test Tools: Post a message to #core in Slack when a workflow fails.

This adds an additional step to each GitHub Action workflow file that posts a message to #core in Slack every time a workflow run fails.

A minor test and spacing change is included in this commit in order to that messages are posted correctly and will be reverted after testing.

See #52644.

git-svn-id: https://develop.svn.wordpress.org/trunk@51511 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/functions.php

@@ -27,7 +27,7 @@ class Tests_Functions extends WP_UnitTestCase {
 		$this->assertSame( array(), wp_parse_args( $a ) );
 		$b = array(
 			'_baba' => 5,
-			'yZ'    => 'baba',
+			'yZ'    => 'bab',
 			'a'     => array( 5, 111, 'x' ),
 		);
 		$this->assertSame(