Revert cache to use github.ref instead of github.sha

.github/workflows/documentation.yml

@@ -50,7 +50,7 @@ jobs:
         uses: actions/cache@v3
         id: cache
         with:
-          key: mkdocs-material-${{ github.sha }}
+          key: mkdocs-material-${{ github.ref }}
           path: .cache
           restore-keys: |
             mkdocs-material-

docs/publishing-your-site.md

@@ -40,11 +40,11 @@ contents:
               python-version: 3.x
           - uses: actions/cache@v3
             with:
-              key: mkdocs-material-${{ github.sha }}
+              key: mkdocs-material-${{ github.ref }} # (3)!
               path: .cache
               restore-keys: |
                 mkdocs-material-
-          - run: pip install mkdocs-material # (3)!
+          - run: pip install mkdocs-material # (4)!
           - run: mkdocs gh-deploy --force
     ```
 
@@ -53,7 +53,10 @@ contents:
     2.  At some point, GitHub renamed `master` to `main`. If your default branch
         is named `master`, you can safely remove `main`, vice versa.
 
-    3.  This is the place to install further [MkDocs plugins] or Markdown
+    3.  The `github.ref` property assures that the cache will
+        update on each pull request merge.
+
+    4.  This is the place to install further [MkDocs plugins] or Markdown
         extensions with `pip` to be used during the build:
 
         ``` sh
@@ -85,7 +88,7 @@ contents:
               python-version: 3.x
           - uses: actions/cache@v3
             with:
-              key: mkdocs-material-${{ github.sha }}
+              key: mkdocs-material-${{ github.ref }}
               path: .cache
               restore-keys: |
                 mkdocs-material-

docs/setup/ensuring-data-privacy.md

@@ -501,7 +501,7 @@ carried out. You might want to:
               python-version: 3.x
           - uses: actions/cache@v3
             with:
-              key: mkdocs-material-${{ github.sha }}
+              key: mkdocs-material-${{ github.ref }}
               path: .cache
               restore-keys: |
                 mkdocs-material-

docs/setup/setting-up-social-cards.md

@@ -249,7 +249,7 @@ whether the social cards need to be regenerated. You might want to:
               python-version: 3.x
           - uses: actions/cache@v3
             with:
-              key: mkdocs-material-${{ github.sha }}
+              key: mkdocs-material-${{ github.ref }}
               path: .cache
               restore-keys: |
                 mkdocs-material-