test: fix next-after-app-static (#94195)
This test has been flaking in weird ways, but i also noticed that it's a
bit broken
- we were running build twice, because `next.start()` does that. this
affected what was in the logs that we assert on
- The assertion on the route was incorrect (it checked for `[page]
/static/route` instead of `[route] /static/route`, which would never be
emitted)
- ...which was hiding the fact that actually the thing *was* getting
logged due to a bug unrelated to after()
The idea in the test was essentially to assert that no after()s run at
runtime if the page/route is statically prerendered (which implicitly
also asserts that `after` itself does not make it dynamic). But it
appears that returning a `new Response()` from a static handler is
unsupported (bug imho) because it logs `Failed to update prerender cache
for /static/route Error: LRUCache: calculateSize returned 0, but size
must be > 0. Items with size 0 would never be evicted, causing unbounded
cache growth.`. As a workaround, i just gave it a non-empty body
I don't know if this will fix the flakes we've been seeing in CI. Those,
bizarrely, fail here
```
Error: can not run export while server is running, use next.stop() first
at NextStartInstance.build (/__w/next.js/next.js/test/lib/next-modes/next-start.ts:255:13)
at Object.build (/__w/next.js/next.js/test/e2e/app-dir/next-after-app-static/build-time/build-time.test.ts:36:36)
```
https://github.com/vercel/next.js/blob/1bc1da711cd0699b620716b204b480485274ff05/test/e2e/app-dir/next-after-app-static/build-time/build-time.test.ts#L36
We do `skipStart` in `nextTestSetup`, and there's no other tests running, so i have no idea what "running server" that error is referring to
