Flaky test: `TestCaptcha`

[silverwind]

Seen here:

--- FAIL: TestCaptcha (5.97s)
    --- FAIL: TestCaptcha/Success (5.00s)
        hcaptcha_test.go:76: Post "https://hcaptcha.com/siteverify": context deadline exceeded (Client.Timeout exceeded while awaiting headers)
FAIL