Bump actions/setup-dotnet from 1.9.0 to 2 (#88)

Bumps [actions/setup-dotnet](https://github.com/actions/setup-dotnet) from 1.9.0 to 2.
- [Release notes](https://github.com/actions/setup-dotnet/releases)
- [Commits](actions/setup-dotnet@v1.9.0...v2)

---
updated-dependencies:
- dependency-name: actions/setup-dotnet
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/build.yml

@@ -30,7 +30,7 @@ jobs:
     runs-on: ${{ matrix.runs-on }}
     steps:
       - name: Setup .NET Core SDK
-        uses: actions/setup-dotnet@v1.9.0
+        uses: actions/setup-dotnet@v2
         with:
           dotnet-version: |
             3.1.x