Fix SurfaceSyncGroupTests

SurfaceSyncGroupTest was using a stub transaction for SurfaceSyncGroup,
but was not resetting it to the real Transaction when the test was
complete. This made the following test that was expecting to use real
Transactions fail.

Fixes: 279141968
Test: SurfaceSyncGroupTest SurfaceSyncGroupTests
Change-Id: Ifa1122ff9d74c8850b8c46216846a4e1b73f4c1c

services/tests/wmtests/src/com/android/server/wm/SurfaceSyncGroupTest.java

@@ -32,6 +32,7 @@ import androidx.test.filters.SmallTest;
 
 import com.android.server.testutils.StubTransaction;
 
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -52,6 +53,11 @@ public class SurfaceSyncGroupTest {
         SurfaceSyncGroup.setTransactionFactory(StubTransaction::new);
     }
 
+    @After
+    public void tearDown() {
+        SurfaceSyncGroup.setTransactionFactory(SurfaceControl.Transaction::new);
+    }
+
     @Test
     public void testSyncOne() throws InterruptedException {
         final CountDownLatch finishedLatch = new CountDownLatch(1);