Explicitly enabled Proguard compat for NearbyMultiDevicesClientsSnippets

This target statically links MessageNano, colliding with the system
version of that class. Normally this is resolved through jarjar, but
as a test, and with shrinking/optimization disabled, this collision
should be benign. Enable R8 compat mode to treat the failure as a
warning.

Bug: 215530220
Change-Id: Id09d839dbe2ef7e2f98e6a79f1338078f1b24378
Test: m NearbyMultiDevicesClientsSnippets
Ignore-AOSP-First: nearby_not_in_aosp_yet
diff --git a/nearby/tests/multidevices/clients/Android.bp b/nearby/tests/multidevices/clients/Android.bp
index b1bf9a7..db6d191 100644
--- a/nearby/tests/multidevices/clients/Android.bp
+++ b/nearby/tests/multidevices/clients/Android.bp
@@ -41,6 +41,9 @@
     optimize: {
         enabled: true,
         shrink: false,
+        // Required to avoid class collisions from static and shared linking
+        // of MessageNano.
+        proguard_compatibility: true,
         proguard_flags_files: ["proguard.flags"],
     },
 }