Update actions/checkout action to v4 (#23)

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

Author: renovate[bot]

.github/workflows/build.yml

@@ -26,7 +26,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Install .NET SDKs
       uses: actions/setup-dotnet@v1.9.0
       with:
@@ -56,7 +56,7 @@ jobs:
     needs: build
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Download coverage reports
       uses: actions/download-artifact@v4
     - name: Install ReportGenerator tool