test: adapt test-v8-serdes for V8 9.9

V8 changed the serialization format so we cannot expect that a value
serialized by an old version can be reserialized to the same bytes.
Change the test to expect that deserialization of the old value still
works.

Add another test which is expected to fail when the format changes so
that we are aware when it happens and can call it out in the release
notes.

Closes: #41519

test/parallel/test-v8-serdes.js

@@ -155,18 +155,41 @@ const hostObject = new (internalBinding('js_stream').JSStream)();
 }
 
 {
+  // Test that an old serialized value can still be deserialized.
   const buf = Buffer.from('ff0d6f2203666f6f5e007b01', 'hex');
 
   const des = new v8.DefaultDeserializer(buf);
   des.readHeader();
+  assert.strictEqual(des.getWireFormatVersion(), 0x0d);
+
+  const value = des.readValue();
+  assert.strictEqual(value, value.foo);
+}
+
+{
+  const message = `New serialization format.
+
+    This test is expected to fail when V8 changes its serialization format.
+    When that happens, the "desStr" variable must be updated to the new value
+    and the change should be mentioned in the release notes, as it is semver-major.
+
+    Consider opening an issue as a heads up at https://github.com/nodejs/node/issues/new
+  `;
+
+  const desStr = 'ff0f6f2203666f6f5e007b01';
+
+  const desBuf = Buffer.from(desStr, 'hex');
+  const des = new v8.DefaultDeserializer(desBuf);
+  des.readHeader();
+  const value = des.readValue();
 
   const ser = new v8.DefaultSerializer();
   ser.writeHeader();
+  ser.writeValue(value);
 
-  ser.writeValue(des.readValue());
-
-  assert.deepStrictEqual(buf, ser.releaseBuffer());
-  assert.strictEqual(des.getWireFormatVersion(), 0x0d);
+  const serBuf = ser.releaseBuffer();
+  const serStr = serBuf.toString('hex');
+  assert.deepStrictEqual(serStr, desStr, message);
 }
 
 {