Bump Microsoft.Testing.Platform.MSBuild from 2.1.0 to 2.2.1 (#233)

Updated
[Microsoft.Testing.Platform.MSBuild](https://github.com/microsoft/testfx)
from 2.1.0 to 2.2.1.

<details>
<summary>Release notes</summary>

_Sourced from [Microsoft.Testing.Platform.MSBuild's
releases](https://github.com/microsoft/testfx/releases)._

## 2.2.1

See release notes
[here](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md#​221---2021-03-01).

## 2.2.0-preview-20210115-03

See release notes
[here](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md#​220-preview-20210115-03---2021-01-20).

## 2.2.0-preview-20201126-03

See release notes
[here](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md#​220-preview-20201126-03---2020-11-26).

## 2.1.2


See release notes
[here](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md#​212---2020-06-08).

## 2.1.1

See release notes
[here](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md#​211---2020-04-01).

Commits viewable in [compare
view](microsoft/testfx@v2.1.0...v2.2.1).
</details>

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tests/PolylineAlgorithm.Tests/PolylineAlgorithm.Tests.csproj

@@ -19,7 +19,7 @@
 		<PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
 		<PackageReference Include="Microsoft.Testing.Extensions.VSTestBridge" Version="2.1.0" />
 		<PackageReference Include="MSTest" Version="4.2.1" />
-		<PackageReference Include="Microsoft.Testing.Platform.MSBuild" Version="2.1.0" />
+		<PackageReference Include="Microsoft.Testing.Platform.MSBuild" Version="2.2.1" />
 		<PackageReference Include="Microsoft.Testing.Extensions.CodeCoverage" Version="18.6.2" />
 		<PackageReference Include="Microsoft.Testing.Extensions.TrxReport" Version="2.2.1" />
 		<PackageReference Include="Microsoft.Extensions.Diagnostics.Testing" Version="10.4.0" />