Bump Akka.TestKit.XUnit2 from 1.4.37 to 1.4.38 (#256)

Bumps [Akka.TestKit.XUnit2](https://github.com/akkadotnet/akka.net) from 1.4.37 to 1.4.38.
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/1.4.38/RELEASE_NOTES.md)
- [Commits](akkadotnet/akka.net@1.4.37...1.4.38)

---
updated-dependencies:
- dependency-name: Akka.TestKit.XUnit2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

src/common.props

@@ -21,7 +21,7 @@
     <NetStandardVersion>netstandard1.6</NetStandardVersion>
     <NetFrameworkLibVersion>net461</NetFrameworkLibVersion>
     <NetFrameworkTestVersion>netcoreapp3.1</NetFrameworkTestVersion>
-    <AkkaVersion>1.4.37</AkkaVersion>
+    <AkkaVersion>1.4.38</AkkaVersion>
     <PbmVersion>0.8.5</PbmVersion>
   </PropertyGroup>
 </Project>