chore(ci): do not publish GitHub releases for nightlies (#28853)

Publishing GitHub releases for each nightly is creating more noise than
the team would like. As a result, we are going to stop publishing the
GitHub release. However, nightly builds will continue to automatically
release. Developers can look at the commits in `main` to determine if a
commit is in a nightly build:
https://github.com/ionic-team/ionic-framework