Fixed GitHub Action cache

Author: kamilkrzyskow

.github/workflows/documentation.yml

@@ -50,8 +50,10 @@ jobs:
         uses: actions/cache@v3
         id: cache
         with:
-          key: ${{ runner.os }}-${{ hashFiles('.cache/**') }}
+          key: mkdocs-material-${{ github.sha }}
           path: .cache
+          restore-keys: |
+            mkdocs-material-
 
       - name: Install dependencies
         run: sudo apt-get install pngquant