GH Actions: bust the cache semi-regularly

.github/workflows/cs.yml

@@ -32,6 +32,9 @@ jobs:
       # @link https://github.com/marketplace/actions/install-composer-dependencies
       - name: Install Composer dependencies
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM.
+          custom-cache-suffix: $(date -u "+%Y-%m")
 
       - name: Check PHP code style
         id: phpcs

.github/workflows/test.yml

@@ -56,13 +56,17 @@ jobs:
       - name: Install Composer dependencies - normal
         if: ${{ matrix.experimental == false }}
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM.
+          custom-cache-suffix: $(date -u "+%Y-%m")
 
       # For the PHP "nightly", we need to install with ignore platform reqs as not all dependencies allow it.
       - name: Install Composer dependencies - with ignore platform
         if: ${{ matrix.experimental == true }}
         uses: "ramsey/composer-install@v2"
         with:
           composer-options: --ignore-platform-reqs
+          custom-cache-suffix: $(date -u "+%Y-%m")
 
       - name: Lint
         run: composer phplint -- --checkstyle | cs2pr
@@ -111,6 +115,9 @@ jobs:
 
       - name: Install Composer dependencies - normal
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM.
+          custom-cache-suffix: $(date -u "+%Y-%m")
 
       - name: Lint
         run: composer phplint -- --checkstyle | cs2pr