Adding computed prop for FOSS merge trains

By adding a computed prop for merge train
helper text, we ensure that if running as
FOSS, we dont render the merge train helper and
this prevent the vue component from breaking.

app/assets/javascripts/vue_merge_request_widget/mixins/ready_to_merge.js

@@ -32,5 +32,8 @@ export default {
     isMergeImmediatelyDangerous() {
       return false;
     },
+    shouldRenderMergeTrainHelperText() {
+      return false;
+    },
   },
 };