Fix GitHub Actions workflow: specify cache-dependency-path for pip caching

Author: jeremymanning

.github/workflows/build-content.yml

@@ -30,6 +30,7 @@ jobs:
         with:
           python-version: '3.11'
           cache: 'pip'
+          cache-dependency-path: 'requirements-build.txt'
 
       - name: Install dependencies
         run: pip install -r requirements-build.txt