[ci] Wait for the preview tarballs before running the deploy tests (#96527)
The "Test new and changed tests when deployed" jobs install Next.js from
the preview tarballs built for the commit under test, but nothing made
them wait for those tarballs to exist. Until #96438 the job was ordered
behind `test-prod` and the other new-test jobs, which delayed it long
enough that the tarballs had usually landed by the time it looked for
them. Now that it starts immediately it frequently fails with "Artifacts
not found for commit ...".
The ordering cannot be expressed as a `needs:` entry, because the
tarballs are published by a different workflow and, for pull requests
from branches in this repository, a different event than the
`build-and-test` run that consumes them. We therefore add a
`wait-for-preview-tarball` job that polls for the tarball instead, and
make both deploy test jobs depend on it. Doing the waiting in one cheap
job keeps the deploy test matrices off their 16-core runners until there
is something for them to install.
The new job is also listed in `tests-pass`. A dependency failure skips
the jobs that need it, and a skipped job does not count as a failure, so
without that entry a tarball that never arrives would have let the
required check pass with the deploy tests never having run.
`test-new-tests-deploy-cache-components` gets the same treatment,
dropping the incidental ordering it still inherited from
`test-cache-components-prod` and picking up the docs-only guard that
`test-new-tests-deploy` already had.
next.js
c00449d5 - [ci] Wait for the preview tarballs before running the deploy tests (#96527)
