Bump AkkaVersion from 1.4.19 to 1.4.20
Bump AkkaVersion from 1.4.19 to 1.4.20

Bumps `AkkaVersion` from 1.4.19 to 1.4.20.

Updates `Akka` from 1.4.19 to 1.4.20
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/dev/RELEASE_NOTES.md)
- [Commits](https://github.com/akkadotnet/akka.net/compare/1.4.19...1.4.20)

Updates `Akka.Serialization.Hyperion` from 1.4.19 to 1.4.20
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/dev/RELEASE_NOTES.md)
- [Commits](https://github.com/akkadotnet/akka.net/compare/1.4.19...1.4.20)

Updates `Akka.TestKit.Xunit2` from 1.4.19 to 1.4.20
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/dev/RELEASE_NOTES.md)
- [Commits](https://github.com/akkadotnet/akka.net/compare/1.4.19...1.4.20)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
akkadotnet/Hyperion,akkadotnet/Hyperion