Use $this->getServiceContainer() tests

Consistently use
	$this->getServiceContainer()
instead of
	MediaWikiServices::getInstance()
in tests.

Change-Id: I409e4c25b301c9110348bedb7f4457030bbc17e5

tests/phpunit/CategoryTreeServiceWiringTest.php

@@ -5,8 +5,6 @@
  * as it could not be included as it's in another extension.
  */
 
-use MediaWiki\MediaWikiServices;
-
 /**
  * @coversNothing
  */
@@ -15,7 +13,7 @@ class CategoryTreeServiceWiringTest extends MediaWikiIntegrationTestCase {
 	 * @dataProvider provideService
 	 */
 	public function testService( string $name ) {
-		MediaWikiServices::getInstance()->get( $name );
+		$this->getServiceContainer()->get( $name );
 		$this->addToAssertionCount( 1 );
 	}