patch 8.2.1201: Vim9: crash when passing number as dict key

Problem:    Vim9: crash when passing number as dict key.
Solution:   Check key type to be string. (closes #6449)

src/testdir/test_vim9_func.vim

@@ -954,6 +954,14 @@ def Test_filter_return_type()
   assert_equal(6, res)
 enddef
 
+def Wrong_dict_key_type(items: list<number>): list<number>
+  return filter(items, {_, val -> get({val: 1}, 'x')})
+enddef
+
+def Test_wrong_dict_key_type()
+  assert_fails('Wrong_dict_key_type([1, 2, 3])', 'E1029:')
+enddef
+
 def Line_continuation_in_def(dir: string = ''): string
     let path: string = empty(dir)
             \ ? 'empty'

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1201,
 /**/
     1200,
 /**/

src/vim9compile.c

@@ -3212,6 +3212,7 @@ compile_lambda_call(char_u **arg, cctx_T *cctx)
 compile_dict(char_u **arg, cctx_T *cctx, int literal)
 {
     garray_T	*instr = &cctx->ctx_instr;
+    garray_T	*stack = &cctx->ctx_type_stack;
     int		count = 0;
     dict_T	*d = dict_alloc();
     dictitem_T	*item;
@@ -3254,10 +3255,16 @@ compile_dict(char_u **arg, cctx_T *cctx, int literal)
 
 	    if (compile_expr0(arg, cctx) == FAIL)
 		return FAIL;
-	    // TODO: check type is string
 	    isn = ((isn_T *)instr->ga_data) + instr->ga_len - 1;
 	    if (isn->isn_type == ISN_PUSHS)
 		key = isn->isn_arg.string;
+	    else
+	    {
+		type_T *keytype = ((type_T **)stack->ga_data)
+							   [stack->ga_len - 1];
+		if (need_type(keytype, &t_string, -1, cctx, FALSE) == FAIL)
+		    return FAIL;
+	    }
 	}
 
 	// Check for duplicate keys, if using string keys.