chore(deps): update actions/checkout action to v6 (#77)

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

Author: renovate[bot]

.github/workflows/main.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
     # install deps
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: install debian-packaged dependencies
       run: sudo apt install -y libgtest-dev libbenchmark-dev libfmt-dev tidy git python3 python3-dateutil pipx
     - name: install pypi-packaged dependencies
@@ -53,7 +53,7 @@ jobs:
 
     steps:
     # install deps
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: install debian-packaged dependencies
       run: sudo apt install -y libgtest-dev libbenchmark-dev libfmt-dev tidy git python3 python3-dateutil python3-pip
     - name: install pypi-packaged dependencies
@@ -78,7 +78,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Build Docker image (no push)
       uses: mr-smithers-excellent/docker-build-push@v6
       with: