Reduce warnings on CI from GitHub Actions (#5083)

* 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

.github/actions/binary-compatible-builds/action.yml

@@ -2,7 +2,7 @@ name: 'Set up a CentOS 6 container to build releases in'
 description: 'Set up a CentOS 6 container to build releases in'
 
 runs:
-  using: node12
+  using: node16
   main: 'main.js'
 inputs:
   name:

.github/actions/github-release/action.yml

@@ -8,5 +8,5 @@ inputs:
     description: ''
     required: true
 runs:
-  using: 'node12'
+  using: 'node16'
   main: 'main.js'

.github/actions/install-rust/action.yml

@@ -8,5 +8,5 @@ inputs:
     default: 'stable'
 
 runs:
-  using: node12
+  using: node16
   main: 'main.js'