Bump MSTest.TestFramework from 2.2.10 to 3.1.1 in /src

Bumps [MSTest.TestFramework](https://github.com/microsoft/testfx) from 2.2.10 to 3.1.1.
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Changelog](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md)
- [Commits](microsoft/testfx@v2.2.10...v3.1.1)

---
updated-dependencies:
- dependency-name: MSTest.TestFramework
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

src/Ankh.VS.UnitTest/Ankh.VS.UnitTest.csproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <Import Project="../tools/Ankh-Common.targets" />
@@ -109,7 +109,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.VSSDK.UnitTestLibrary" Version="14.3.25407" />
     <PackageReference Include="Moq" Version="4.18.2" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
+    <PackageReference Include="MSTest.TestFramework" Version="3.1.1" />
     <PackageReference Include="NUnit" Version="3.13.3" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />