Bump Microsoft.Reactive.Testing from 4.3.2 to 4.4.1 (#289)

Bumps [Microsoft.Reactive.Testing](https://github.com/dotnet/reactive) from 4.3.2 to 4.4.1.
- [Release notes](https://github.com/dotnet/reactive/releases)
- [Commits](dotnet/reactive@rxnet-v4.3.2...rxnet-v4.4.1)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Directory.Build.targets

@@ -35,7 +35,7 @@
         <PackageReference Update="coverlet.msbuild" Version="2.9.0" />
         <PackageReference Update="System.Reactive" Version="4.4.1" />
         <PackageReference Update="System.Collections.Immutable" Version="1.7.1" />
-        <PackageReference Update="Microsoft.Reactive.Testing" Version="4.3.2" />
+        <PackageReference Update="Microsoft.Reactive.Testing" Version="4.4.1" />
         <PackageReference Update="MediatR" Version="8.0.1" />
         <PackageReference Update="MediatR.Extensions.Microsoft.DependencyInjection" Version="8.0.0" />
         <PackageReference Update="Bogus" Version="29.0.1" />