rabbit_db_bindings: Explicitly mark exists_in_khepri tx as read-only

This is essentially a cosmetic change. Read-only transactions are done
with queries in Khepri rather than commands, like read-write
transactions. Local queries cannot timeout like commands so marking the
transaction as 'ro' means that we don't need to handle a potential
'{error, timeout}' return.

(cherry picked from commit fe28028)
(cherry picked from commit 703fa38)

Author: the-mikedavis

deps/rabbit/src/rabbit_db_binding.erl

@@ -120,7 +120,7 @@ exists_in_khepri(#binding{source = SrcName,
                        Errs ->
                            Errs
                    end
-           end) of
+           end, ro) of
         {ok, not_found} -> false;
         {ok, Set} -> sets:is_element(Binding, Set);
         Errs -> not_found_errs_in_khepri(not_found(Errs, SrcName, DstName))