Bump AkkaVersion from 1.5.6 to 1.5.7

Bumps `AkkaVersion` from 1.5.6 to 1.5.7.

Updates `Akka` from 1.5.6 to 1.5.7
- [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@1.5.6...1.5.7)

Updates `Akka.TestKit.Xunit2` from 1.5.6 to 1.5.7
- [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@1.5.6...1.5.7)

Updates `Akka.Cluster` from 1.5.6 to 1.5.7
- [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@1.5.6...1.5.7)

---
updated-dependencies:
- dependency-name: Akka
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: Akka.TestKit.Xunit2
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: Akka.Cluster
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

src/common.props

@@ -16,7 +16,7 @@
     <XunitRunnerVersion>2.4.5</XunitRunnerVersion>
     <TestSdkVersion>17.6.0</TestSdkVersion>
     <NBenchVersion>2.0.1</NBenchVersion>
-    <AkkaVersion>1.5.6</AkkaVersion>
+    <AkkaVersion>1.5.7</AkkaVersion>
     <NetCoreTestVersion>netcoreapp3.1</NetCoreTestVersion>
     <NetFrameworkTestVersion>net471</NetFrameworkTestVersion>
     <NetStandardLibVersion>netstandard2.0</NetStandardLibVersion>