testing/postgresql-pg_variables: upgrade to 1.2.5_git20230922
https://github.com/postgrespro/pg_variables/compare/9f9466c...67b5121
Also resolves a rebuild error with gcc 14.
https://github.com/postgrespro/pg_variables/compare/9f9466c...67b5121
Also resolves a rebuild error with gcc 14.