ThumbnailEntryPointTest: Set named user in context

Why:

- The default uploader is the context user, which defaults to an
  anonymous user, and that will fail with temp accounts enabled

What:

- Set a default context user as a named test user account

Bug: T365669
Change-Id: I75eb63e359cd4db01a89ab6c952cc221b54c6dba

tests/phpunit/includes/filerepo/ThumbnailEntryPointTest.php

@@ -33,6 +33,9 @@ class ThumbnailEntryPointTest extends MediaWikiIntegrationTestCase {
 	 * will be called only once per test class
 	 */
 	public function addDBDataOnce() {
+		// Set a named user account for the request context as the default,
+		// so that these tests do not fail with temp accounts enabled
+		RequestContext::getMain()->setUser( $this->getTestUser()->getUser() );
 		// Create mock repo with test files
 		$this->initTestRepoGroup();