rpc: add explicit 200 response for empty HTTP GET (#20952)

rpc/http.go

@@ -208,6 +208,7 @@ func (t *httpServerConn) SetWriteDeadline(time.Time) error { return nil }
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Permit dumb empty requests for remote health-checks (AWS)
 	if r.Method == http.MethodGet && r.ContentLength == 0 && r.URL.RawQuery == "" {
+		w.WriteHeader(http.StatusOK)
 		return
 	}
 	if code, err := validateRequest(r); err != nil {