Update actions/checkout action to v6 (#26)

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

Author: renovate[bot]

.github/workflows/publish.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     environment: release
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-dotnet@v5

.github/workflows/tests.yaml

@@ -13,7 +13,7 @@ jobs:
   check-pre-commit:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: "3.13"
@@ -22,7 +22,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-dotnet@v5
         with:
           dotnet-version: |