Update @covers tags of LanguageSearchTest

That second class (which is generated by the LanguageNameIndexer script)
is an integral part of the class under test.

Change-Id: I7d8dc66b4d1e86684e0de3e585d9e0a544640159

tests/phpunit/LanguageSearchTest.php

@@ -19,7 +19,8 @@
  */
 
 /**
- * @covers LanguageNameSearch
+ * @covers \LanguageNameSearch
+ * @covers \LanguageNameSearchData
  */
 class LanguageSearchTest extends PHPUnit\Framework\TestCase {
 	/**