net/http: TestTransportEventTrace_h2 fails with "expected substring "WroteRequest: {Err:<nil>}" in output." after the fix of #15744

[mikioh]

See https://build.golang.org/log/8ea5a0e40dc6649089f2038d09f7d1aa33a0b801

--- FAIL: TestTransportEventTrace_h2 (0.05s)
    transport_test.go:3306: expected substring "WroteRequest: {Err:<nil>}" in output.
    transport_test.go:3329: Output:
        Getting conn for dns-is-faked.golang:55935 ...
        DNS start: {Host:dns-is-faked.golang}
        DNS done: {Addrs:[{IP:127.0.0.1 Zone:}] Err:<nil> Coalesced:false}
        ConnectStart: Connecting to tcp 127.0.0.1:55935 ...
        ConnectDone: connected to tcp 127.0.0.1:55935 = <nil>
        got conn: {Conn:0xc4203b8900 Reused:false WasIdle:false IdleTime:0s}
        Wait100Continue
        first response byte
        Got100Continue
        first response byte
        got roundtrip.response
        consumed body
FAIL
FAIL    net/http    17.453s

[gopherbot]

CL https://golang.org/cl/23284 mentions this issue.