Update actions/checkout action to v6

| datasource  | package          | from   | to     |
| ----------- | ---------------- | ------ | ------ |
| github-tags | actions/checkout | v5.0.1 | v6.0.0 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/continuous-integration.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v5.0.1
+      - uses: actions/checkout@v6.0.0
       - uses: shivammathur/setup-php@2.35.5
 
         with: