feat: HTTP add TLS fingerprint fallback (#1444)

pkg/download/engine/testdata/wpt/fetch/api/response/response-headers-guard.any.js

@@ -0,0 +1,8 @@
+// META: global=window,worker
+// META: title=Response: error static method
+
+promise_test (async () => {
+  const response = await fetch("../resources/data.json");
+  assert_throws_js(TypeError, () => { response.headers.append("name", "value"); });
+  assert_not_equals(response.headers.get("name"), "value", "response headers should be immutable");
+}, "Ensure response headers are immutable");