Remove SkipMainlinePresubmit annotation from testIsPrivateDnsBroken.

testIsPrivateDnsBroken isn't flaky any more, remove the
SkipMainlinePresubmit annotation.

Bug: 289879947
Test: atest ConnectivityManagerTest#testIsPrivateDnsBroken --iterations 100
Change-Id: I402153fa09144a96a500c96ecf7c89f41702bd0d
diff --git a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
index 0e926cc..c2feaab 100644
--- a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
+++ b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
@@ -213,7 +213,6 @@
 import com.android.testutils.DeviceInfoUtils;
 import com.android.testutils.DumpTestUtils;
 import com.android.testutils.RecorderCallback.CallbackEntry;
-import com.android.testutils.SkipMainlinePresubmit;
 import com.android.testutils.SkipPresubmit;
 import com.android.testutils.TestHttpServer;
 import com.android.testutils.TestNetworkTracker;
@@ -1032,7 +1031,6 @@
 
     @AppModeFull(reason = "WRITE_SECURE_SETTINGS permission can't be granted to instant apps")
     @Test @IgnoreUpTo(Build.VERSION_CODES.Q)
-    @SkipMainlinePresubmit(reason = "Out of SLO flakiness")
     public void testIsPrivateDnsBroken() throws InterruptedException {
         final String invalidPrivateDnsServer = "invalidhostname.example.com";
         final String goodPrivateDnsServer = "dns.google";