8284585: PushPromiseContinuation test fails intermittently in timeout

.../share/classes/jdk/internal/net/http/Http2Connection.java

...dk/java/net/httpclient/http2/PushPromiseContinuation.java

.../httpclient/test/lib/http2/Http2TestServerConnection.java

...ib/jdk/httpclient/test/lib/http2/OutgoingPushPromise.java