tests: update MSTest to version 3.1.1 (#218)

Author: Meir017

src/FluentAssertions.Analyzers.Tests/FluentAssertions.Analyzers.Tests.csproj

@@ -13,8 +13,8 @@
     </PackageReference>
     <PackageReference Include="FluentAssertions" Version="6.1.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.3.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="2.0.0" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.0.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="3.1.1" />
+    <PackageReference Include="MSTest.TestFramework" Version="3.1.1" />
     <PackageReference Include="xunit.assert" Version="2.4.2" />
   </ItemGroup>