Fix typo, noticed by Will Crawford.

src/backend/utils/adt/json.c

@@ -87,7 +87,7 @@ static void array_to_json_internal(Datum array, StringInfo result, bool use_line
 /* fake type category for JSON so we can distinguish it in datum_to_json */
 #define TYPCATEGORY_JSON 'j'
 /* letters appearing in numeric output that aren't valid in a JSON number */
-#define NON_NUMERIC_LETTER "NnAnIiFfTtYy"
+#define NON_NUMERIC_LETTER "NnAaIiFfTtYy"
 /*
  * Input.
  */