Drop PostgreSQL version 12 support

Author: kovmir

.github/workflows/installcheck.yml

@@ -13,11 +13,11 @@ jobs:
     strategy:
       matrix:
         pgversion:
+          - 17
           - 16
           - 15
           - 14
           - 13
-          - 12
 
     env:
       PGVERSION: ${{ matrix.pgversion }}

postgresql_extension_template.c

@@ -4,7 +4,7 @@
 PG_MODULE_MAGIC;
 
 /* Abost compilation against unsupported versions. */
-#if PG_VERSION_NUM < 120000
+#if PG_VERSION_NUM < 130000
 #error "Unsupported PostgreSQL Version"
 #endif