chore(ci): add Node.js setup step in GitHub Actions workflow for staking

- Introduced a new step to set up Node.js version 20.x in the contracts-staking-hardhat-tests.yml workflow.
- Configured caching for npm dependencies to optimize build times.

Author: Seth-Schmidt

.github/workflows/contracts-staking-hardhat-tests.yml

@@ -29,6 +29,13 @@ jobs:
         with:
           persist-credentials: 'false'
 
+      - name: Setup Node
+        uses: actions/setup-node@60edb5dd545a775178f52524783378180af0d1f8 # v4.0.2
+        with:
+          node-version: 20.x
+          cache: npm
+          cache-dependency-path: contracts/staking/package-lock.json
+
       - name: Install dependencies
         working-directory: contracts/staking
         run: npm ci