fix(lro): clarify protobuf response for no parallel requests

For protobuf guidance, it was unclear response code should be.

aep/general/0151/aep.md.j2

@@ -75,10 +75,23 @@ but is not obligated to do so:
 
 - Resources that accept multiple parallel requests **may** place them in a
   queue rather than work on the requests simultaneously.
-- Resource that does not permit multiple requests in parallel (denying any new
-  request until the one that is in progress finishes) **must** return
-  `409 Conflict` if a user attempts a parallel request, and include an error
-  message explaining the situation.
+
+{% tab proto %}
+
+- A Resource that does not permit multiple requests in parallel (denying any new
+  request until the one that is in progress finishes) **must** return `ABORTED`
+  if a user attempts a parallel request, and include an error message explaining
+  the situation.
+
+{% tab oas %}
+
+- A Resource that does not permit multiple requests in parallel (denying any new
+  request until the one that is in progress finishes) **must** return a `409
+  Conflict` if a user attempts a parallel request, and include an error message
+  explaining the situation.
+
+{% endtabs %}
+
 
 ### Expiration