patch 8.1.1821: no test for wrong number of method arguments

Problem:    No test for wrong number of method arguments.
Solution:   Add a test.
diff --git a/src/version.c b/src/version.c
index b0d9481..aad7833 100644
--- a/src/version.c
+++ b/src/version.c
@@ -774,6 +774,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1821,
+/**/
     1820,
 /**/
     1819,