ci: update actions (#137)

This change aims to fix the following deprecation warning:

```
Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: actions/checkout, actions/setup-node, actions/setup-node, actions/checkout
```

See https://github.com/prettier/stylelint-config-prettier/actions/runs/3423941045

.github/workflows/main.yml

@@ -24,8 +24,8 @@ jobs:
           - 12
           - 11
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
         with:
           node-version: ${{ matrix.node-version }}
       - run: npm install