Use Enums for logical replication message types at more places.
Commit
644f0d7cc9 added logical replication message type enums to use
instead of character literals but some char substitutions were overlooked.
Author: Peter Smith
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAHut+PsTG=Vrv8hgrvOnAvCNR21jhqMdPk2n0a1uJPoW0p+UfQ@mail.gmail.com