Bump Akka.Cluster.Sharding in /src/clustering/sharding-sqlserver (#188)

Bumps [Akka.Cluster.Sharding](https://github.com/akkadotnet/akka.net) from 1.5.20 to 1.5.21.
- [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@1.5.20...1.5.21)

---
updated-dependencies:
- dependency-name: Akka.Cluster.Sharding
  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.Build.props

@@ -16,7 +16,7 @@
     <NetRuntime>net8.0</NetRuntime>
     <XunitVersion>2.4.2</XunitVersion>
     <TestSdkVersion>17.6.0</TestSdkVersion>
-    <AkkaVersion>1.5.20</AkkaVersion>
+    <AkkaVersion>1.5.21</AkkaVersion>
     <PbmVersion>1.4.1</PbmVersion>
     <AkkaHostingVersion>1.5.20</AkkaHostingVersion>
     <MicrosoftExtensionsVersion>[8.0.0,)</MicrosoftExtensionsVersion>