Also set $wgContLang in MWITC::setContentLang()

This assignment got lost in change Ie7a89f6ed7 (commit 47464abb4f) – the
resetServices() now implicit in setMwGlobals() resets the
ContentLanguage service, but does not update the $wgContLang global.
setService( 'ContentLanguage' ) does update it, but that method is
deliberately not used in this branch of setContentLang(), for reasons
that I assume are still relevant even though the comment explaining them
was removed – see change I8c60e37c17 (commit c70c2e4714).

Bug: T231630
Change-Id: I0170cc6bf40a5524523c45e8ffff8f72adc2fc47

tests/phpunit/MediaWikiIntegrationTestCase.php

@@ -1122,7 +1122,10 @@ abstract class MediaWikiIntegrationTestCase extends PHPUnit\Framework\TestCase {
 			$this->setService( 'ContentLanguage', $lang );
 			$this->setMwGlobals( 'wgLanguageCode', $lang->getCode() );
 		} else {
-			$this->setMwGlobals( 'wgLanguageCode', $lang );
+			$this->setMwGlobals( [
+				'wgLanguageCode' => $lang,
+				'wgContLang' => Language::factory( $lang ),
+			] );
 		}
 	}