remove deprecated set-env from pipeline

Author: martinothamar

.github/workflows/dotnet-core.yml

@@ -26,7 +26,7 @@ jobs:
       run: dotnet test --no-restore --verbosity normal
     - name: Get version
       if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/')
-      run: echo "::set-env name=VERSION::$(git describe --tags --dirty)"
+      run: echo "VERSION=$(git describe --tags --dirty)" >> $GITHUB_ENV
     - name: Pack
       if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/')
       run: dotnet pack -c Release -o artifacts/ -p:Version=$VERSION