[auth] Fix auth_provider error code.

I believe this is the cause of the spurious internal error we've been
finding in our logs. If the view gets closed on us that not our fault
and so auth provider shouldn't be declaring an internal error (which
gets converted by token manager into another internal error).

Change-Id: I746a8e5550bae100a6fee4121fae29b3152ac9f8
diff --git a/auth_providers/google/google_auth_provider_impl.cc b/auth_providers/google/google_auth_provider_impl.cc
index 3d233a6..5bed4ed 100644
--- a/auth_providers/google/google_auth_provider_impl.cc
+++ b/auth_providers/google/google_auth_provider_impl.cc
@@ -165,7 +165,7 @@
   auth_ui_context_.set_error_handler([this](zx_status_t status) {
     FX_LOG(INFO, NULL, "Overlay cancelled by the caller");
     ReleaseResources();
-    get_persistent_credential_callback_(AuthProviderStatus::INTERNAL_ERROR,
+    get_persistent_credential_callback_(AuthProviderStatus::UNKNOWN_ERROR,
                                         nullptr, nullptr);
     return;
   });