Set exported to true to allow external adb to start app for CI (flutter#92118)

Author: GaryQian

dev/integration_tests/deferred_components_test/android/app/src/main/AndroidManifest.xml

@@ -16,7 +16,7 @@ found in the LICENSE file. -->
         <activity
             android:name=".MainActivity"
             android:launchMode="singleTop"
-            android:exported="false"
+            android:exported="true"
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"