t/oxr_android: Fix manifest by specifying the full classname of the activity

Needed in order to fix the move of the default namespace.

src/xrt/targets/openxr_android/src/main/AndroidManifest.xml

@@ -41,7 +41,7 @@
     <uses-permission android:name="android.permission.HIGH_SAMPLING_RATE_SENSORS" />
 
     <application
-        android:name=".MonadoOpenXrApplication"
+        android:name="org.freedesktop.monado.openxr_runtime.MonadoOpenXrApplication"
         android:allowBackup="true"
         android:extractNativeLibs="true"
         android:icon="@drawable/ic_monado_logo"