chore(tests): Enable testing on node.js v18.x on GitHub CI (#6619)

* chore(tests): Enable testing on node.js v18.x on GitHub CI

* chore(tests): Remove outdated calls to test:prepare npm script

The calls to `npm run test:prepare` in `tests/scripts/setup_*_env.sh`
should have been removed along with that npm script in PR #4906.

* chore(deps): Fix alphabetisation in package.json

.github/workflows/build.yml

@@ -17,8 +17,9 @@ jobs:
         # TODO (#2114): re-enable osx build.
         # os: [ubuntu-latest, macos-latest]
         os: [ubuntu-latest]
-        node-version: [14.x, 16.x]
-        # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
+        node-version: [14.x, 16.x, 18.x]
+        # See supported Node.js release schedule at
+        # https://nodejs.org/en/about/releases/
 
     steps:
     - uses: actions/checkout@v3