Move the build to .net 5 (#2294)

* Move the build to .net 5

.NET 5 is fine for building projects that target older versions of .NET. This also should fix the AppVeyor build which fails because the latest `coverlet.console` only supports .NET 5.

* Some things need .NET core 3.1 available

Co-authored-by: Brendan Forster <github@brendanforster.com>

.github/workflows/netcore.yml

@@ -19,9 +19,14 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
+    - name: Setup .NET 5
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 5.0.*
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
-
+      with:
+        dotnet-version: 3.1.*
     - name: Build with dotnet
       run: ./build.sh --linksources=true --verbosity=verbose
       shell: bash

.github/workflows/publish.yml

@@ -14,6 +14,8 @@ jobs:
     - uses: actions/checkout@v1
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 5.0.*
 
     - name: Build with dotnet
       run: ./build.sh --linksources=true --verbosity=verbose