Several PGXN modules reference LockTagType values; renumbering would
force a recompile of those modules. Oversight in back-patch of today's
commit 566372b3d6. Back-patch to released
branches, v12 through 9.5.
Reported by Tom Lane.
Discussion: https://postgr.es/m/921383.1597523945@sss.pgh.pa.us