chore: pin GitHub Actions to commit SHAs (#433)

Files updated: gh-pages.yml

Pinned actions:
  - actions/checkout@de0fac2 # v6.0.2
  - actions/setup-node@49933ea # v4
  - aws-actions/configure-aws-credentials@7474bc4 # v4

All `uses:` references now point to immutable commit SHAs.
Version tags are preserved in trailing comments for readability.

Author: liam-icheng-lai

.github/workflows/gh-pages.yml

@@ -32,11 +32,11 @@ jobs:
     steps:
       # Checkout code
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2 https://github.com/actions/checkout/releases/tag/v6.0.2
 
       # Set up Node.js environment
       - name: Setup Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4 https://github.com/actions/setup-node/releases/tag/v4
         with:
           node-version: '22.3'
           cache: 'npm'
@@ -72,7 +72,7 @@ jobs:
           npm run build
 
       - name: Configure AWS credentials
-        uses: aws-actions/configure-aws-credentials@v4
+        uses: aws-actions/configure-aws-credentials@7474bc4690e29a8392af63c5b98e7449536d5c3a # v4 https://github.com/aws-actions/configure-aws-credentials/releases/tag/v4
         with:
           role-to-assume: arn:aws:iam::${{ matrix.account }}:role/gha-s3-frontend-deployment
           role-session-name: gha-s3-frontend-deployment