minor #368 Update GitHub Actions checkout to v5 (OskarStark)

This PR was merged into the main branch.

Discussion
----------

 Update GitHub Actions checkout to v5

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Docs?         | no
| Issues        | --
| License       | MIT

Update all workflow files to use actions/checkout@v5 instead of v4

Commits
-------

b6b62cf Update GitHub Actions checkout to v5

Author: OskarStark

.github/workflows/code-quality.yaml

@@ -24,7 +24,7 @@ jobs:
                 php-version: [ '8.4' ]
         steps:
             - name: Checkout
-              uses: actions/checkout@v4
+              uses: actions/checkout@v5
 
             - name: Configure environment
               run: |

.github/workflows/doctor-rst.yaml

@@ -16,7 +16,7 @@ jobs:
         runs-on: ubuntu-latest
         steps:
             - name: Checkout
-              uses: actions/checkout@v4
+              uses: actions/checkout@v5
 
             - name: Create cache dir
               run: mkdir .cache

.github/workflows/unit-tests.yaml

@@ -38,7 +38,7 @@ jobs:
             SYMFONY_REQUIRE: ${{ matrix.symfony-version || '>=6.4' }}
 
         steps:
-            - uses: actions/checkout@v4
+            - uses: actions/checkout@v5
 
             - name: Configure environment
               run: |