Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/docker.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Clone the repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Read version from ref
         id: version

.github/workflows/main.yml

@@ -31,7 +31,7 @@ jobs:
       DOTNET_CLI_TELEMETRY_OPTOUT: 1
       NUGET_PACKAGES: ${{ github.workspace }}/.github/nuget-packages
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up .NET SDK
         uses: actions/setup-dotnet@v5
 
@@ -50,14 +50,14 @@ jobs:
   encoding:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Verify encoding
         shell: pwsh
         run: scripts/Test-Encoding.ps1
   licenses:
     runs-on: ubuntu-24.04
     steps:
       - name: Check out the sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: REUSE license check
         uses: fsfe/reuse-action@v6

.github/workflows/release.yml

@@ -27,7 +27,7 @@ jobs:
         run: echo "version=$(if ($env:GITHUB_REF.StartsWith('refs/tags/v')) { $env:GITHUB_REF -replace '^refs/tags/v', '' } else { 'next' })" >> $env:GITHUB_OUTPUT
 
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Read the changelog
         uses: ForNeVeR/ChangelogAutomation.action@v2