Upgrade .NET Core version used in builds

.github/workflows/build.yml

@@ -33,7 +33,7 @@ jobs:
         uses: actions/setup-dotnet@v1
         with:
           # As usual, obtained from: https://dotnetcli.blob.core.windows.net/dotnet/release-metadata/5.0/releases.json
-          dotnet-version: "3.1.404" # since we now use this
+          dotnet-version: "3.1.409" # since we now use this
       - name: Clear Nuget Cache
         run: dotnet nuget locals all --clear
       - name: Restore

.github/workflows/docs.yml

@@ -30,7 +30,7 @@ jobs:
         uses: actions/setup-dotnet@v1
         with:
           # As usual, obtained from: https://dotnetcli.blob.core.windows.net/dotnet/release-metadata/5.0/releases.json
-          dotnet-version: "3.1.404" # since we now use this
+          dotnet-version: "3.1.409" # since we now use this
       - name: Clear Nuget Cache
         run: dotnet nuget locals all --clear
       - name: Nuget Restore

Common.props

@@ -11,5 +11,9 @@
     <AnalysisMode>AllEnabledByDefault</AnalysisMode>
     <AnalysisLevel>latest</AnalysisLevel>
   </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.2" />
+  </ItemGroup>
   
 </Project>