pg_buffercache: add sql test

When Who What
2022-07-30 19:40:14 Tom Lane (tgl) Added tgl as reviewer
2022-07-30 19:40:12 Tom Lane (tgl) Closed in commitfest 2022-07 with status: Committed
2022-07-30 19:40:12 Tom Lane (tgl) Changed committer to tgl
2022-06-07 00:37:12 DongWook Lee (dongwooklee) Changed targetversion to None
2022-06-06 13:34:35 DongWook Lee (dongwooklee) Changed authors to DongWook Lee (dongwooklee)
2022-06-06 13:34:35 DongWook Lee (dongwooklee) Changed targetversion to 15
2022-06-06 13:33:33 DongWook Lee (dongwooklee) Attached mail thread CAAcByaLCHGJB7qAENEcx9D09UL=w4ma+yijwF_-1MSqQZ9wK6Q@mail.gmail.com
2022-06-06 13:33:33 DongWook Lee (dongwooklee) Created patch record