Bump System.Reactive from 4.1.5 to 4.1.6
Bump System.Reactive from 4.1.5 to 4.1.6

Bumps [System.Reactive](https://github.com/dotnet/reactive) from 4.1.5 to 4.1.6.
- [Release notes](https://github.com/dotnet/reactive/releases)
- [Commits](https://github.com/dotnet/reactive/compare/rxnet-v4.1.5...rxnet-v4.1.6)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
PKRoma/refit