Fix stale featureName in ReleaseNoteHeader test (#5009)

serverlessWorkers was split into serverlessWorkersLambda and
serverlessWorkersCloudRun in featureReleaseTypes.js, so the old key no
longer resolved and the test fell back to the explicit type prop
instead of overriding it.

Author: Duncanma

tests/test-mdx-to-md.mjs

@@ -663,7 +663,7 @@ test("ReleaseNoteHeader resolves label from featureName in paired form", () => {
 });
 
 test("ReleaseNoteHeader featureName overrides explicit type when mapped", () => {
-  const input = `<ReleaseNoteHeader featureName="serverlessWorkers" type="publicPreview">\nBody.\n</ReleaseNoteHeader>`;
+  const input = `<ReleaseNoteHeader featureName="serverlessWorkersCloudRun" type="publicPreview">\nBody.\n</ReleaseNoteHeader>`;
   const { markdown } = transformMdx(input);
   assertContains(markdown, "> **Pre-release**");
 });