Add another SQL/JSON error code

A code comment said that the standard does not define a number for
ERRCODE_SQL_JSON_ITEM_CANNOT_BE_CAST_TO_TARGET_TYPE, but this was
fixed in a later draft version of the standard, so use that number
now.

src/backend/executor/execExprInterp.c

@@ -4980,13 +4980,7 @@ ExecEvalJsonExpr(ExprEvalStep *op, ExprContext *econtext,
 					 * type simply does not exist.
 					 */
 					ereport(ERROR,
-
-					/*
-					 * XXX Standard says about a separate error code
-					 * ERRCODE_SQL_JSON_ITEM_CANNOT_BE_CAST_TO_TARGET_TYPE but
-					 * does not define its number.
-					 */
-							(errcode(ERRCODE_SQL_JSON_SCALAR_REQUIRED),
+							(errcode(ERRCODE_SQL_JSON_ITEM_CANNOT_BE_CAST_TO_TARGET_TYPE),
 							 errmsg("SQL/JSON item cannot be cast to target type")));
 				}
 				else if (!jcstate->estate)

src/backend/utils/errcodes.txt

@@ -222,6 +222,7 @@ Section: Class 22 - Data Exception
 2203D    E    ERRCODE_TOO_MANY_JSON_ARRAY_ELEMENTS                           too_many_json_array_elements
 2203E    E    ERRCODE_TOO_MANY_JSON_OBJECT_MEMBERS                           too_many_json_object_members
 2203F    E    ERRCODE_SQL_JSON_SCALAR_REQUIRED                               sql_json_scalar_required
+2203G    E    ERRCODE_SQL_JSON_ITEM_CANNOT_BE_CAST_TO_TARGET_TYPE            sql_json_item_cannot_be_cast_to_target_type
 
 Section: Class 23 - Integrity Constraint Violation