feat(mtls): Fix import and test

Author: andyrzhao

oauth2_http/java/com/google/auth/mtls/SecureConnectProvider.java

@@ -41,6 +41,7 @@
 import java.io.InputStream;
 import java.security.GeneralSecurityException;
 import java.security.KeyStore;
+import java.util.concurrent.TimeUnit;
 import java.util.List;
 
 /**

oauth2_http/javatests/com/google/auth/mtls/SecureConnectProviderTest.java

@@ -142,7 +142,7 @@ public void testRunCertificateProviderCommandTimeout() throws InterruptedExcepti
             () -> SecureConnectProvider.runCertificateProviderCommand(certCommandProcess, 100));
     assertTrue(
         "expected to fail with timeout",
-        actual.getMessage().contains("cert provider command timed out"));
+        actual.getMessage().contains("Cert provider command timed out"));
   }
 
   @Test