* Upgrade our github actions to "node16"
Each github actions run has a lot of warnings about using node12 so this
upgrades our repository to using node16. I'm hoping no other changes are
needed and I suspect other actions we're using are on node12 and will
need further updates, but this should help pin down what's remaining.
* Update `actions/checkout` workflow to `v3`
* Update to `actions/cache@v3`
* Update to `actions/upload-artifact@v3`
* Drop usage of `actions-rs/toolchain`
* Update to `actions/setup-python@v4`
* Update mdbook version
Before this commit we actually have two builders checking for security
advisories on CI, one is `cargo audit` and one is `cargo deny`. The
`cargo deny` builder is slightly different in that it checks a few other
things about our dependency tree such as licenses, duplicates, etc. This
commit removes the advisory check from `cargo deny` on CI and then moves
the `cargo audit` check to a separate workflow.
The `cargo audit` check will now run nightly and will open an issue on
the Wasmtime repository when an advisory is found. This should help make
it such that our CI is never broken by the publication of an advisory
but we're still promptly notified whenever an advisory is made. I've
updated the release process notes to indicate that the open issues
should be double-checked to ensure that there are no open advisories
that we need to take care of.
