build(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/dotnet.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
     - name: Checkout Source Code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Setup .NET
       uses: actions/setup-dotnet@v4

.github/workflows/publish-to-nuget.yml

@@ -14,7 +14,7 @@ jobs:
       SOLUTION: 'Atypical.VirtualFileSystem.sln'
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup .NET SDK
         uses: actions/setup-dotnet@v4
@@ -43,7 +43,7 @@ jobs:
       BUILD_CONFIG: 'Release'
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup .NET SDK
         uses: actions/setup-dotnet@v4
@@ -58,7 +58,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Get Build Version
         run: |