Update to /external/robolectric rather than older /external/robolectric-shadows

Bug: 261728063
Test: atest of soong robolectric module
Change-Id: Ia6297abf3a189e89bb90bdc8f6a4af5e69968da8
diff --git a/tests/robotests/Android.bp b/tests/robotests/Android.bp
index 1b170c0..5821367 100644
--- a/tests/robotests/Android.bp
+++ b/tests/robotests/Android.bp
@@ -19,4 +19,5 @@
     ],
 
     instrumentation_for: "MmsService",
+    upstream: true,
 }