it looks like the good folks over at actix-web found an error in h2spec section 3.5

actix/actix-web#1453

"Clients and servers MUST treat an invalid connection preface as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. A GOAWAY frame (Section 6.8) MAY be omitted in this case, since an invalid preface indicates that the peer is not using HTTP/2." per http2 sec https://http2.github.io/http2-spec/#ConnectionHeader

but it looks like h2spec requires a GOAWAY frame--please see the linked issue