Remove nightly release (backport #3479)

[mergify]

I recently switched on immutable releases which broke our nightly release. I think the best solution is to stop doing the nightly release. The build artifacts can be found by checking the recent workflow runs, so it's unnecessary to also upload them as a release.

I also added sigstore to the workflow to sign the builds.

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This is an automatic backport of pull request #3479 done by Mergify.

[mergify]

Cherry-pick of 1d39f64 has failed:

On branch mergify/bp/0.28.x/pr-3479
Your branch is up to date with 'origin/0.28.x'.

You are currently cherry-picking commit 1d39f640.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/workflows/release.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally