Sync PG_VERSION file in CREATE DATABASE.
An OS crash could leave PG_VERSION empty or missing. The same symptom
appeared in a backup by block device snapshot, taken after the next
checkpoint and before the OS flushes the PG_VERSION blocks. Device
snapshots are not a documented backup method, however. Back-patch to
v15, where commit
9c08aea6a3090a396be334cc58c511edab05776a introduced
STRATEGY=WAL_LOG and made it the default.
Discussion: https://postgr.es/m/
20240130195003.0a.nmisch@google.com