Update actions/checkout version.

Author: bgrainger

.github/workflows/publish-package.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: 'windows-latest'
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
 
     - name: Set up .NET 6.0
       uses: actions/setup-dotnet@v1