prep CI for net8.0 upgrade (#120)

* bump dotnet in runner

* delete empty file

* fix tests

.github/workflows/build_and_publish.yml

@@ -14,7 +14,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '2.2.x'
+        dotnet-version: '8.0.x'
     - name: Restore
       run: dotnet restore
     - name: Build with dotnet
@@ -37,6 +37,6 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '2.2.x'
+        dotnet-version: '8.0.x'
     - name: Publish the library
       run: dotnet nuget push artifact/*.nupkg -s https://api.nuget.org/v3/index.json -k ${{ secrets.NUGET_API_KEY }} -n --skip-duplicate

GoCardless.Tests/GoCardless.Tests.csproj

@@ -1,12 +1,12 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="4.19.2" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
     <PackageReference Include="NUnit" Version="3.7.1" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.8.0-alpha1" />
   </ItemGroup>