Fix prerender tags when notFound is called (#74577)

This ensures we don't lose tags added to a page before `notFound()` is
called as otherwise a fetch on the page that has been revalidated won't
be able to be applied correctly if dropped from a `notFound()` call.
This was broken recently in the refactors of handling rendering in
app-render as it worked correctly in `v14`.

x-ref: [slack
thread](https://vercel.slack.com/archives/C04V3E1UYNQ/p1736200963684869)

Closes https://linear.app/vercel/issue/ENET-1381
Closes https://linear.app/vercel/issue/NEXT-3946
Closes #73973
Closes #66540

Author: ijjk

packages/next/src/server/app-render/app-render.tsx

@@ -3777,7 +3777,7 @@ async function prerenderToStream(
       revalidate: INFINITE_CACHE,
       expire: INFINITE_CACHE,
       stale: INFINITE_CACHE,
-      tags: [...implicitTags],
+      tags: [...(prerenderStore?.tags || implicitTags)],
     })
     const errorRSCPayload = await workUnitAsyncStorage.run(
       prerenderLegacyStore,