H2 Clear-Text protocol error on upgrade to spring-cloud 2021.0.1

Describe the bug
We have our api gateway configured to use http2 (http2: server.http2.enabled= true)

• spring-cloud: 2021.0.0

After upgrading to spring-cloud 2021.0.1 we get a netty protocol exception.
Downgrading again to 2021.0.0 solves the problem.

**Stacktrace**:
[fullstacktrace.txt](https://github.com/spring-cloud/spring-cloud-gateway/files/8443260/stacktrace.txt)

java.lang.IllegalArgumentException: Configured H2 protocol without TLS. Use H2 Clear-Text protocol via HttpClient#protocol or configure TLS via HttpClient#secure
	at reactor.netty.http.client.HttpClientConnect$MonoHttpConnect.lambda$subscribe$0(HttpClientConnect.java:251) ~[reactor-netty-http-1.0.15.jar:1.0.15]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	*__checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.authorization.AuthorizationWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.authorization.ExceptionTranslationWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.authe
ntication.logout.LogoutWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.savedrequest.ServerRequestCacheWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.context.SecurityContextServerWebExchangeWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.context.ReactorContextWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.header.HttpHeaderWriterWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.config.web.server.ServerHttpSecurity$ServerWebExchangeReactorContextWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.security.web.server.WebFilterChainProxy [DefaultWebFilterChain]
	*__checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ HTTP POST "/api/xxxxx" [ExceptionHandlingWebHandler]

Start with the linked fullstacktrace.txt and the Reactor Netty HttpClient#protocol and HttpClient#secure entry points, comparing behavior between Spring Cloud 2021.0.0 and 2021.0.1. Done means the configured HTTP/2 gateway no longer raises the clear-text protocol exception after upgrading, with the behavior verified against the reported setup.