patch 8.2.2531: Vim9: the :k command is obscure

Problem:    Vim9: the :k command is obscure.
Solution:   Disallow using :k, can use :mark instead. (closes #7874)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 84c9108..c75ead9 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -8520,6 +8520,7 @@
 	    case CMD_append:
 	    case CMD_change:
 	    case CMD_insert:
+	    case CMD_k:
 	    case CMD_t:
 	    case CMD_xit:
 		    not_in_vim9(&ea);