net/http/httptest: TestServer failures with `Unexpected response after close`

[bcmills]

#!watchflakes
post <- pkg == "net/http/httptest" && test == "TestServer" && `[Uu]nexpected response after close`

https://build.golang.org/log/8c4d32d4bbf0da2fa412f833d30a774d5e83c9d6:

--- FAIL: TestServer (0.27s)
    --- FAIL: TestServer/NewServer (0.04s)
        --- FAIL: TestServer/NewServer/GetAfterClose (0.01s)
            server_test.go:98: Unexpected response after close: 404 Not Found, map[Content-Length:[19] Content-Type:[text/plain; charset=utf-8] Date:[Tue, 06 Dec 2022 23:47:03 GMT] X-Content-Type-Options:[nosniff]], 404 page not found
FAIL
FAIL	net/http/httptest	0.548s

[bcmills]

(CC @neild)

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "net/http/httptest" && test == "TestServer" && `[Uu]nexpected response after close`

2022-12-06 22:07 openbsd-arm64-jsing go@e535d677 net/http/httptest.TestServer (log)

--- FAIL: TestServer (0.27s)
    --- FAIL: TestServer/NewServer (0.04s)
        --- FAIL: TestServer/NewServer/GetAfterClose (0.01s)
            server_test.go:98: Unexpected response after close: 404 Not Found, map[Content-Length:[19] Content-Type:[text/plain; charset=utf-8] Date:[Tue, 06 Dec 2022 23:47:03 GMT] X-Content-Type-Options:[nosniff]], 404 page not found

— watchflakes

[gopherbot]

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)