Set the volatility of the timestamptz version of date_bin() back to immutable

543f36b43d was too hasty in thinking that the volatility of date_bin()
had to match date_trunc(), since only the latter references
session_timezone.

Bump catversion

Per feedback from Aleksander Alekseev
Backpatch to v14, as the former commit was

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202108311
+#define CATALOG_VERSION_NO	202109031
 
 #endif

src/include/catalog/pg_proc.dat

@@ -5844,7 +5844,7 @@
   proargtypes => 'interval timestamp timestamp', prosrc => 'timestamp_bin' },
 { oid => '6178',
   descr => 'bin timestamp with time zone into specified interval',
-  proname => 'date_bin', provolatile => 's', prorettype => 'timestamptz',
+  proname => 'date_bin', prorettype => 'timestamptz',
   proargtypes => 'interval timestamptz timestamptz',
   prosrc => 'timestamptz_bin' },