Explicitly export the main activity of the test apk

A new requirement for 31

Bug: 190588547
Test: TARGET_BUILD_APPS=com.android.virt m; adb install <path>; adb
reboot
Change-Id: If03b6cb5eb64694cebaa56d037ead611d18d9b17

Change-Id: Ibe293169f39b74ec34b490dd216030c1d7221588
diff --git a/tests/testapk/AndroidManifest.xml b/tests/testapk/AndroidManifest.xml
index 05ebb4e..74ae206 100644
--- a/tests/testapk/AndroidManifest.xml
+++ b/tests/testapk/AndroidManifest.xml
@@ -15,7 +15,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
       package="com.android.microdroid.test">
     <application android:label="Microdroid Test">
-        <activity android:name="TestActivity">
+        <activity android:name="TestActivity" android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />