Improve support for UNICODE collation on older ICU

The recently added standard collation UNICODE (0d21d4b9bc) doesn't
give consistent results on some build farm members with old ICU
versions.  Apparently, the ICU locale specification 'und' (language
tag style) misbehaves on some older ICU versions.  Replacing it with
'' (ICU locale ID style) fixes it at least on some OS versions.  Let's
see what the build farm says.

src/bin/initdb/initdb.c

@@ -1498,7 +1498,7 @@ setup_collation(FILE *cmdfd)
 	 * that they win if libc defines a locale with the same name.
 	 */
 	PG_CMD_PRINTF("INSERT INTO pg_collation (oid, collname, collnamespace, collowner, collprovider, collisdeterministic, collencoding, colliculocale)"
-				  "VALUES (pg_nextoid('pg_catalog.pg_collation', 'oid', 'pg_catalog.pg_collation_oid_index'), 'unicode', 'pg_catalog'::regnamespace, %u, '%c', true, -1, 'und');\n\n",
+				  "VALUES (pg_nextoid('pg_catalog.pg_collation', 'oid', 'pg_catalog.pg_collation_oid_index'), 'unicode', 'pg_catalog'::regnamespace, %u, '%c', true, -1, '');\n\n",
 				  BOOTSTRAP_SUPERUSERID, COLLPROVIDER_ICU);
 
 	PG_CMD_PRINTF("INSERT INTO pg_collation (oid, collname, collnamespace, collowner, collprovider, collisdeterministic, collencoding, collcollate, collctype)"

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202303101
+#define CATALOG_VERSION_NO	202303131
 
 #endif