test_runner: avoid reusing V8 serializers

lib/internal/test_runner/reporter/v8-serializer.js

@@ -9,11 +9,12 @@ const { serializeError } = require('internal/error_serdes');
 
 
 module.exports = async function* v8Reporter(source) {
-  const serializer = new DefaultSerializer();
-  serializer.writeHeader();
-  const headerLength = TypedArrayPrototypeGetLength(serializer.releaseBuffer());
+  const headerSerializer = new DefaultSerializer();
+  headerSerializer.writeHeader();
+  const headerLength = TypedArrayPrototypeGetLength(headerSerializer.releaseBuffer());
 
   for await (const item of source) {
+    const serializer = new DefaultSerializer();
     const originalError = item.data.details?.error;
     if (originalError) {
       // Error is overridden with a serialized version, so that it can be

test/parallel/test-runner-v8-deserializer.mjs

@@ -85,6 +85,15 @@ describe('v8 deserializer', common.mustCall(() => {
     assert.deepStrictEqual(reported, [reportedDiagnosticEvent]);
   });
 
+  it('should serialize a repeated object as independent messages', async () => {
+    const repeatedChunks = await toArray(serializer([diagnosticEvent, diagnosticEvent]));
+    const reported = await collectReported(repeatedChunks);
+    assert.deepStrictEqual(reported, [
+      reportedDiagnosticEvent,
+      reportedDiagnosticEvent,
+    ]);
+  });
+
   it('should deserialize a serialized chunk after non-serialized chunk', async () => {
     const reported = await collectReported([Buffer.concat([Buffer.from('unknown'), ...chunks])]);
     assert.deepStrictEqual(reported, [