In jsonb_plpython.c, suppress warning message from gcc 10.

Very recent gcc complains that PLyObject_ToJsonbValue could return
a pointer to a local variable.  I think it's wrong; but the coding
is fragile enough, and the savings of one palloc() minimal enough,
that it seems better to just do a palloc() all the time.  (My other
idea of tweaking the if-condition doesn't suppress the warning.)

Back-patch to v11 where this code was introduced.

Discussion: https://postgr.es/m/21547.1580170366@sss.pgh.pa.us

contrib/jsonb_plpython/jsonb_plpython.c

@@ -410,7 +410,6 @@ PLyNumber_ToJsonbValue(PyObject *obj, JsonbValue *jbvNum)
 static JsonbValue *
 PLyObject_ToJsonbValue(PyObject *obj, JsonbParseState **jsonb_state, bool is_elem)
 {
-	JsonbValue	buf;
 	JsonbValue *out;
 
 	if (!(PyString_Check(obj) || PyUnicode_Check(obj)))
@@ -421,10 +420,6 @@ PLyObject_ToJsonbValue(PyObject *obj, JsonbParseState **jsonb_state, bool is_ele
 			return PLyMapping_ToJsonbValue(obj, jsonb_state);
 	}
 
-	/* Allocate JsonbValue in heap only if it is raw scalar value. */
-	if (*jsonb_state)
-		out = &buf;
-	else
 	out = palloc(sizeof(JsonbValue));
 
 	if (obj == Py_None)