fix(parser): reject an array-of-tables header extending a frozen inline table

Assisted-by: GLM 5.3

interpres_test.go

@@ -487,6 +487,9 @@ func TestRejectsInlineTableExtension(t *testing.T) {
 		"by header":      "a = { b = 1 }\n[a.c]\nx = 2\n",
 		"by dotted key":  "a = { b = 1 }\na.c = 2\n",
 		"header over it": "a = { b = 1 }\n[a]\nx = 2\n",
+		// The frozen check must cover the intermediate steps of an array-of-tables
+		// header, not only the leaf: [[a.b.c]] walks through a and a.b.
+		"by nested array header": "a = { b = {} }\n[[a.b.c]]\nx = 2\n",
 	}
 	for name, doc := range cases {
 		if _, err := Parse([]byte(doc)); err == nil {