modifications for pg16 but not enough

[PerikAdjust]

Start of some modifications to past pg16 test but still doesn't work:

I continue to investigate to find solution but I do not see anything corresponding with the error in pg16 changelog.

• I started to do some needed change

#if PG_VERSION_NUM >= 160000
#include "varatt.h"
#endif

I also changed ltree.h with the delete of the use of function DatumGetPointer (after look at the different errors), I also do some test so I'm not sure that's useful. That why I keep the previous version commented.

FYI: with docker act to test locally the workflow, each test past except: CI / 🐘 PostgreSQL 16 (pull_request)