Fix JSONACTION_RETURN_SUCCESS definition on pg16-

On postgres 15 and below, pgsptokentype is defined to void rather than an
actual enum, so a lot of functions don't return anything.  But an empty
JSONACTION_RETURN_SUCCESS define doesn't exit the function as it would with
pg16+ definition, which leads to bogus behavior.  To fix, simply define
JSONACTION_RETURN_SUCCESS to "return" on pg 15 and below.

pgsp_json.c

@@ -29,7 +29,7 @@
 #if PG_VERSION_NUM < 160000
 #include "parser/gram.h"
 #define JsonParseErrorType void
-#define JSONACTION_RETURN_SUCCESS()
+#define JSONACTION_RETURN_SUCCESS() return
 #else
 /* In PG16, include/scan.h was gone. Define required symbols manually.. */
 /* must be in sync with src/backend/parser/gram.h */