Disable flaky app pair assertions

Assertion is flaky in presubmit

Bug: 186510496
Test: atest FlickerTests WMShellFlickerTests
Change-Id: Ic796c86d555376283adbcdb06ea80c6d9ddbfe07

libs/WindowManager/Shell/tests/flicker/src/com/android/wm/shell/flicker/apppairs/AppPairsTransition.kt

@@ -22,6 +22,7 @@ import android.platform.test.annotations.Presubmit
 import android.system.helpers.ActivityHelper
 import android.util.Log
 import android.view.Surface
+import androidx.test.filters.FlakyTest
 import androidx.test.platform.app.InstrumentationRegistry
 import com.android.compatibility.common.util.SystemUtil
 import com.android.server.wm.flicker.FlickerBuilderProvider
@@ -138,7 +139,7 @@ abstract class AppPairsTransition(protected val testSpec: FlickerTestParameter)
         append("$primaryApp $secondaryApp")
     }
 
-    @Presubmit
+    @FlakyTest(bugId = 186510496)
     @Test
     open fun navBarLayerIsAlwaysVisible() {
         testSpec.navBarLayerIsAlwaysVisible()