patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/insexpand.c b/src/insexpand.c
index 3cefb39..d006135 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2746,7 +2746,7 @@
 	return;
 
     if (argvars[1].v_type != VAR_LIST || argvars[1].vval.v_list == NULL)
-	emsg(_(e_invarg));
+	emsg(_(e_invalid_argument));
     else
     {
 	startcol = (int)tv_get_number_chk(&argvars[0], NULL);