ci: add node-stream test coverage workflow (#89861)
## Summary
Run existing app-dir tests with `__NEXT_USE_NODE_STREAMS=true` in CI to
validate the node stream rendering path alongside the default web stream
path.
- New CI job in `build_and_test.yml` that runs a curated set of app-dir
tests with the flag enabled
- `test/use-node-streams-tests-manifest.json`: manifest of tests to run
in node-stream mode
## Test plan
- [x] CI job triggers and runs tests successfully
- [x] Does not affect existing CI jobs
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Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
