Update actions/checkout action to v5

| datasource  | package          | from | to |
| ----------- | ---------------- | ---- | -- |
| github-tags | actions/checkout | v4   | v5 |

Author: renovate[bot]

.github/workflows/continuous-integration.yml

@@ -51,7 +51,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v4"
+        uses: "actions/checkout@v5"
 
       - name: "Install PHP"
         uses: "shivammathur/[email protected]"

.github/workflows/release-on-milestone-closed.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v4"
+        uses: "actions/checkout@v5"
 
       - name: "Release"
         uses: "laminas/automatic-releases@v1"