patch 8.2.4012: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move the last error messages to errors.h.
diff --git a/src/json.c b/src/json.c
index c9bbac6..e19bc97 100644
--- a/src/json.c
+++ b/src/json.c
@@ -1004,8 +1004,7 @@
 			&& dict_find(top_item->jd_tv.vval.v_dict,
 						 top_item->jd_key, -1) != NULL)
 		{
-		    semsg(_("E938: Duplicate key in JSON: \"%s\""),
-							     top_item->jd_key);
+		    semsg(_(e_duplicate_key_in_json_str), top_item->jd_key);
 		    clear_tv(cur_item);
 		    retval = FAIL;
 		    goto theend;