Merge pull request #173 from nils-a/bugfix/GH-172

(GH-172) added missing .NET versions

Author: nils-a

.github/workflows/build.yaml

@@ -50,6 +50,8 @@ jobs:
       - uses: actions/setup-dotnet@3447fd6a9f9e57506b15f895c5b76d3b197dc7c2 # v3.2.0
         with:
           dotnet-version: |
+            2.1.818
+            3.1.x
             5.0.x
             6.0.x
             7.0.x