apiversion properties aren't always applied to RestClient

[philwebb]

A property like this with service works:
spring.http.client.service.apiversion.insert.header=X-API-Version

The same with restclient doesn't:
spring.http.client.restclient.apiversion.insert.header=X-Version

Reproducer

https://github.com/belyaev-andrey/demo-http-client

[belyaev-andrey]

Even removing X- prefix from the header as per spring-projects/spring-framework#35494 doesn't help