net/http: flaky TestH12_RequestContentLength_Known_NonZero

[bradfitz]

Just noticed:

https://build.golang.org/log/31bace9ed1c8e96d66019498ea7538fe78cddedd

...
--- FAIL: TestH12_RequestContentLength_Known_NonZero (0.00s)
    clientserver_test.go:185: HTTP/2 request: Post https://127.0.0.1:56615: http2: stream closed
FAIL
FAIL    net/http    9.285s
...

Maybe it's another case of #16029 in which case this test could just be made more robust.

[bradfitz]

After a bunch of time trying to reproduce this and reading the code again, it looks like this was fixed via golang/net@3797cd8 which was 9 days before this bug report, but that commit wasn't bundled into std until 66b4743, two days after this bug report.

So all good. (famous last words)