Eager load the GraphQL schema in specs

Avoid counting on Rails eager loading the GraphQL types, but preload
them before the specs.

This would avoid loading the schema in 2 separate threads
concurrently (1 inside the specs, 1 inside the test-server that will
receive requests). Loading the schema in parallel like that could
cause duplicate definition errors.

spec/support/helpers/graphql_helpers.rb

@@ -197,3 +197,7 @@ module GraphqlHelpers
     allow(GitlabSchema).to receive(:max_query_depth).with(any_args).and_return nil
   end
 end
+
+# This warms our schema, doing this as part of loading the helpers to avoid
+# duplicate loading error when Rails tries autoload the types.
+GitlabSchema.graphql_definition