Upgrade actions/checkout and use new output command (#3067)

This PR fixes various deprecation messages in CI:
```
The following actions use a deprecated Node.js version and will be forced to run on node20: actions/checkout@v3. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/
```

```
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
```

Resolves: WATonomous/infra-config#2263

.github/workflows/build.yml

@@ -15,18 +15,18 @@ jobs:
         node-version: [20.x,21.x]
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
 
     - name: Set up Python
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@f677139bbe7f9c59b41e40162b753c062f5d49a3 # v5.2.0
       with:
         python-version: '3.11'
 
     - name: Install Python dependencies
       run: pip install -r requirements.txt
 
     - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v3
+      uses: actions/setup-node@1e60f620b9541d16bece96c5465dc8ee9832be0b # v4.0.3
       with:
         node-version: ${{ matrix.node-version }}