chore: Fix logging test

Author: lqiu96

oauth2_http/javatests/com/google/auth/oauth2/LoggingTest.java

@@ -433,6 +433,7 @@ public void sign_sameAs() throws IOException {
   public void getRequestMetadata_hasAccessToken() throws IOException {
     TestAppender testAppender = setupTestLogger(ComputeEngineCredentials.class);
     MockMetadataServerTransportFactory transportFactory = new MockMetadataServerTransportFactory();
+    transportFactory.transport.setServiceAccountEmail("[email protected]");
     ComputeEngineCredentials credentials =
         ComputeEngineCredentials.newBuilder().setHttpTransportFactory(transportFactory).build();
     Map<String, List<String>> metadata = credentials.getRequestMetadata(CALL_URI);