rabbit_db_vhost: Declare no-return in create_or_get/3 spec

`create_or_get_in_khepri/2` throws errors like the
`rabbit_khepri:timeout_error()`. Callers of `create_or_get/3` like
`rabbit_vhost:do_add/3` and its callers handle the throw with a `try`/
`catch` block and return the error tuple, which is then handled by
their callers.

(cherry picked from commit e459ee5)

Author: the-mikedavis

deps/rabbit/src/rabbit_db_vhost.erl

@@ -62,7 +62,7 @@
       VHostName :: vhost:name(),
       Limits :: vhost:limits(),
       Metadata :: vhost:metadata(),
-      Ret :: {existing | new, VHost},
+      Ret :: {existing | new, VHost} | no_return(),
       VHost :: vhost:vhost().
 %% @doc Writes a virtual host record if it doesn't exist already or returns
 %% the existing one.