Coding Standards: Add public visibility to methods in tests/phpunit/includes/.

This commit adds the `public` visibility keyword to each method which did not have an explicit visibility keyword.

Why `public`?

With no visibility previously declared, these methods are implicitly `public` and available for use. As these are part of the WordPress testing framework (for Core and extenders), changing them to anything else would be a backwards-compatibility break.

Props costdev, jrf, hellofromTonya.
See #54177.

git-svn-id: https://develop.svn.wordpress.org/trunk@52009 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/bootstrap.php

@@ -340,7 +340,7 @@ require __DIR__ . '/class-wp-sitemaps-large-test-provider.php';
  */
 class WP_PHPUnit_Util_Getopt {
 
-	function __construct( $argv ) {
+	public function __construct( $argv ) {
 		$skipped_groups = array(
 			'ajax'          => true,
 			'ms-files'      => true,