bump dotnet sdk version to hopefully fix build errors

Author: baronfel

.github/workflows/docs.yml

@@ -12,15 +12,15 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest]
-        dotnet: [3.1.302]
+        dotnet: [5.0.400]
     runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v2
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.201
+        dotnet-version: 5.0.400
     - name: Restore tools
       run: dotnet tool restore
     - name: Restore projects