chore: github actions: up checkout to v6, as v4 is deprecated

.github/workflows/documentation.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install sphinx and prerequisites

.github/workflows/freebsd.yml

@@ -12,7 +12,7 @@ jobs:
     if: ${{ contains(github.event.pull_request.labels.*.name, 'tests:freebsd') }}
     timeout-minutes: 45
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         persist-credentials: false
     - name: Functional tests under FreeBSD

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
         if: ${{ github.event_name == 'pull_request' || inputs.test_type == 'short' }}
         timeout-minutes: 45
         steps:
-        - uses: actions/checkout@v4
+        - uses: actions/checkout@v6
           with:
             persist-credentials: false
         - name: run tests inside a debian12 docker
@@ -38,7 +38,7 @@ jobs:
         if: ${{ contains(github.event.pull_request.labels.*.name, 'tests:long') || inputs.test_type == 'long' }}
         timeout-minutes: 45
         steps:
-        - uses: actions/checkout@v4
+        - uses: actions/checkout@v6
           with:
             persist-credentials: false
         - name: run tests inside a ${{ matrix.platform }} docker
@@ -55,7 +55,7 @@ jobs:
         if: ${{ contains(github.event.pull_request.labels.*.name, 'tests:full') || inputs.test_type == 'full' }}
         timeout-minutes: 45
         steps:
-        - uses: actions/checkout@v4
+        - uses: actions/checkout@v6
           with:
             persist-credentials: false
         - name: run tests inside a ${{ matrix.platform }} docker

.github/workflows/tests_basic.yml

@@ -8,7 +8,7 @@ jobs:
         runs-on: ubuntu-24.04
         timeout-minutes: 10
         steps:
-        - uses: actions/checkout@v4
+        - uses: actions/checkout@v6
           with:
             persist-credentials: false
         - name: install prerequisites