Bump Akka.Cluster.TestKit from 1.5.27.1 to 1.5.28 (#256)

Bumps [Akka.Cluster.TestKit](https://github.com/akkadotnet/akka.net) from 1.5.27.1 to 1.5.28.
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/dev/RELEASE_NOTES.md)
- [Commits](akkadotnet/akka.net@1.5.27.1...1.5.28)

---
updated-dependencies:
- dependency-name: Akka.Cluster.TestKit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <!-- App dependencies -->
   <ItemGroup>
-    <PackageVersion Include="Akka.Cluster.TestKit" Version="1.5.27.1" />
+    <PackageVersion Include="Akka.Cluster.TestKit" Version="1.5.28" />
     <PackageVersion Include="TeamCity.ServiceMessages" Version="4.1.1" />
     <PackageVersion Include="System.CodeDom" Version="8.0.0" />
     <PackageVersion Include="System.Runtime.Loader" Version="4.3.0" />