net/http: fix typo in TestTransportReadToEndReusesConn

The test sets a Content-Type where it looks like it wants a Content-Length. The test passes because the Content-Length header is automatically added anyway, but fix the typo and set Content-Length as intended.

Change-Id: Ic2af778f82c3e9d58e164892f6ac6ef5745f884f
Reviewed-on: https://go-review.googlesource.com/c/go/+/246977
Reviewed-by: Damien Neil <[email protected]>
Trust: Alberto Donizetti <[email protected]>
Trust: Damien Neil <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: KeiichiHirobe

src/net/http/transport_test.go

@@ -412,7 +412,7 @@ func TestTransportReadToEndReusesConn(t *testing.T) {
 			w.WriteHeader(200)
 			w.(Flusher).Flush()
 		} else {
-			w.Header().Set("Content-Type", strconv.Itoa(len(msg)))
+			w.Header().Set("Content-Length", strconv.Itoa(len(msg)))
 			w.WriteHeader(200)
 		}
 		w.Write([]byte(msg))