Sets up Robolectric tests to run as presubmits

In conjunction with cl/494733953, configures ThemePicker
Robolectric tests to run on presubmit at warning level.

Bug: 263483218
Test: atest ThemePickerRoboTests, ABTD test runs
Change-Id: I3ab04daca28634f345cc6c7894e08b9175cb7cc5
diff --git a/tests/robotests/Android.bp b/tests/robotests/Android.bp
index e0a37c2..4416e1c 100644
--- a/tests/robotests/Android.bp
+++ b/tests/robotests/Android.bp
@@ -13,5 +13,8 @@
         "androidx.test.core",
         "androidx.test.runner",
     ],
+
+    upstream: true,
+
     instrumentation_for: "ThemePicker",
 }