[MR extension] Exclude Test MRP in canary build

Tested by building canary build and verifying TestProvider is not compiled into it.

PiperOrigin-RevId: 169451615
diff --git a/init.js b/init.js
index b8dbb5f..3907bf2 100644
--- a/init.js
+++ b/init.js
@@ -44,7 +44,7 @@
  */
 mr.Init.getProviders_ = function(providerManager) {
   const providers = mr.InitHelper.getProviders(providerManager);
-  if (mr.Config.isDebugChannel) {
+  if (!mr.Config.isPublicChannel) {
     providers.push(new mr.TestProvider(providerManager));
   }
   return providers;