khepri_cluster: Use the ?TRANSIENT_ERROR_RETRY_INTERVAL constant

... instead of hard-coding a 200 ms sleep.

[Why]
The same value is used in other retry loops in the same module. It
should have been used there as well.

(cherry picked from commit 77ec77e)

src/khepri_cluster.erl

@@ -878,7 +878,7 @@ wait_for_cluster_change_permitted(RaMemberOrStoreId, Timeout) ->
     %% cluster could have a leader and still not be ready to accept
     %% a cluster change. This avoids too many retries that will
     %% just eat resources.
-    timer:sleep(200),
+    timer:sleep(?TRANSIENT_ERROR_RETRY_INTERVAL),
 
     Ret.