Update actions/checkout action to v3 (#17)

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

.github/workflows/ci-nuget.yml

@@ -10,7 +10,7 @@ jobs:
     timeout-minutes: 15
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
     - name: Set VERSION variable from latest tag (if existing) plus date and commit
       run: | 
         LATEST_TAG=$(git ls-remote --tags origin | tail -n 1 | awk '{ print $2; }' | sed 's/.*v//')