Fix break in master

The break came from the take down of a dotnet feed.

Author: AArnott

nuget.config

@@ -6,6 +6,6 @@
   <packageSources>
     <clear />
     <add key="api.nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
-    <add key="roslyn-analyzers" value="https://dotnet.myget.org/F/roslyn-analyzers/api/v3/index.json" protocolVersion="3" />
+    <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
   </packageSources>
 </configuration>

tests/MessagePackAnalyzer.Tests/MessagePackAnalyzer.Tests.csproj

@@ -14,8 +14,8 @@
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
     <PackageReference Include="coverlet.collector" Version="1.2.0" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.XUnit" Version="1.0.1-beta1.20304.1" />
-    <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.CodeFix.Testing.XUnit" Version="1.0.1-beta1.20304.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.XUnit" Version="1.0.1-beta1.20374.2" />
+    <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.CodeFix.Testing.XUnit" Version="1.0.1-beta1.20374.2" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" version="2.10.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.Workspaces" version="2.10.0" />
   </ItemGroup>