Update actions/checkout action to v6

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

Author: renovate[bot]

.github/workflows/main.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     container: fedorapython/fedora-python-tox:latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install dependencies
         run: |
           dnf install -y git tox libffi-devel
@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
     container: fedorapython/fedora-python-tox:latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           # Needed for diff-cover
           fetch-depth: 0
@@ -58,7 +58,7 @@ jobs:
       - tests-unit
       - tests-misc
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v6
         with: