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/ex_cmds.h b/src/ex_cmds.h
index e82e91b..7888d6f 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -741,7 +741,7 @@
 	EX_TRLBAR|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_NONE),
 EXCMD(CMD_k,		"k",		ex_mark,
-	EX_RANGE|EX_WORD1|EX_TRLBAR|EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK,
+	EX_RANGE|EX_WORD1|EX_TRLBAR|EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK|EX_NONWHITE_OK,
 	ADDR_LINES),
 EXCMD(CMD_keepmarks,	"keepmarks",	ex_wrongmodifier,
 	EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM,