pgstattuple: add test for coverage

When Who What
2022-11-22 22:28:24 Andres Freund (andresfreund) Closed in commitfest 2022-11 with status: Returned with feedback
2022-10-12 08:45:24 Michael Paquier (michael-kun) Closed in commitfest 2022-09 with status: Moved to next CF
2022-10-12 08:45:22 Michael Paquier (michael-kun) New status: Waiting on Author
2022-08-04 09:19:08 Daniel Gustafsson (d_gustafsson) Changed topic to Testing
2022-08-02 01:38:09 DongWook Lee (dongwooklee) Changed authors to DongWook Lee (dongwooklee)
2022-08-02 01:37:44 DongWook Lee (dongwooklee) Attached mail thread CAAcByaKGq2JCBii9Z2MJY0-_phcPsseHS0NOGccGBz77k=FfjA@mail.gmail.com
2022-08-02 01:37:44 DongWook Lee (dongwooklee) Created patch record