Test BasicCurlHttpTests.FinishInAsyncCallback is unstable in CI.

[marcalff]

[ RUN      ] BasicCurlHttpTests.FinishInAsyncCallback
ext/test/http/curl_http_test.cc:525: Failure
Value of: handlers[i]->got_response_
  Actual: false
Expected: true

[  FAILED  ] BasicCurlHttpTests.FinishInAsyncCallback (5 ms)
[----------] 15 tests from BasicCurlHttpTests (7643 ms total)

[----------] Global test environment tear-down
[==========] 15 tests from 1 test suite ran. (7643 ms total)
[  PASSED  ] 14 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] BasicCurlHttpTests.FinishInAsyncCallback

 1 FAILED TEST
===========================================================================

To investigate, unclear if this is a failure due to the test itself, or the production code tested.