Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v5...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>

.github/workflows/default_plugins.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: windows-latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup .NET
         uses: actions/setup-dotnet@v5
         with:

.github/workflows/dotnet.yml

@@ -20,7 +20,7 @@ jobs:
       NUGET_CERT_REVOCATION_MODE: offline
       BUILD_NUMBER: ${{ github.run_number }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set Flow.Launcher.csproj version
         id: update
         uses: vers-one/dotnet-project-version-updater@v1.7

.github/workflows/release_pr.yml

@@ -11,7 +11,7 @@ jobs:
   update-pr:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       
       - uses: actions/setup-python@v6
         with: