patch 8.2.4227: Vim9: using "lockvar!" in :def function does not work

Problem:    Vim9: using "lockvar!" in :def function does not work.
Solution:   Add "!" instead of "-1". (closes #9634)

src/testdir/test_vim9_cmd.vim

@@ -1425,6 +1425,17 @@ def Test_lockvar()
   assert_equal([0, 1, 2], g:therange)
   unlet g:therange
 
+  # use exclamation mark for locking deeper
+  g:nestedlist = [1, [2, 3], 4]
+  lockvar! g:nestedlist
+  try
+    g:nestedlist[1][0] = 9
+  catch /E1119:/
+    caught = true
+  endtry
+  assert_true(caught)
+  unlet g:nestedlist
+
   var d = {a: 1, b: 2}
   d.a = 3
   d.b = 4

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4227,
 /**/
     4226,
 /**/

src/vim9cmds.c

@@ -223,10 +223,12 @@ compile_lock_unlock(
 	ret = FAIL;
     else
     {
-	vim_snprintf((char *)buf, len, "%s %d %s",
-		eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar",
-		deep,
-		p);
+	char *cmd = eap->cmdidx == CMD_lockvar ? "lockvar" : "unlockvar";
+
+	if (deep < 0)
+	    vim_snprintf((char *)buf, len, "%s! %s", cmd, p);
+	else
+	    vim_snprintf((char *)buf, len, "%s %d %s", cmd, deep, p);
 	ret = generate_EXEC_copy(cctx, isn, buf);
 
 	vim_free(buf);