Fix access to underlying request in PlayServerInterpreter

[maxcom]

Play's Request may contain additional context like authentication when it is produced by ActionBuilder. Access to that data was possible it Tapir 0.18.1 by casting ServerRequest.underlying to type that is produced by defaultActionBuilder.

Unfortunately, this was broken in 0.18.3. Fix in #1423 replaced Request with RequestHeader that misses that context.

This pull request provider better fix for #1400, that fixes that problem without affecting underlying. In Play Framework, any Request extends RequestHeader, so this change is backward compatible and should no break code that works with 0.18.3.