Bump Akka from 1.4.11 to 1.4.15

Bumps [Akka](https://github.com/akkadotnet/akka.net) from 1.4.11 to 1.4.15.
- [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@1.4.11...1.4.15)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

src/common.props

@@ -13,7 +13,7 @@ Updated Quartz to 3.0.7</PackageReleaseNotes>
     </NoWarn>
   </PropertyGroup>
   <PropertyGroup>
-    <AkkaVersion>1.4.11</AkkaVersion>
+    <AkkaVersion>1.4.15</AkkaVersion>
     <QuartzVersion>3.2.4</QuartzVersion>
     <XunitVersion>2.4.1</XunitVersion>
     <TestSdkVersion>15.9.0</TestSdkVersion>