Update actions/cache action to v6

| datasource  | package       | from | to     |
| ----------- | ------------- | ---- | ------ |
| github-tags | actions/cache | v5   | v6.0.0 |

Author: renovate[bot]

.github/workflows/continuous-integration.yml

@@ -64,7 +64,7 @@ jobs:
           tools: composer:v2
 
       - name: "Cache dependencies"
-        uses: "actions/cache@v5"
+        uses: "actions/cache@v6"
         with:
           path: |
             ~/.composer/cache
@@ -115,7 +115,7 @@ jobs:
           tools: composer:v2
 
       - name: "Cache dependencies"
-        uses: "actions/cache@v5"
+        uses: "actions/cache@v6"
         with:
           path: |
             ~/.composer/cache