test: reduce impact of flaky HTTP server tests
Mark the tests as flaky on macOS and increase the timeout for other platforms (namely, FreeBSD).
Context: https://github.com/nodejs/node/issues/42741#issuecomment-1113196037
Median success rate (refer to patch and separate tables above):
osx11 freebsd12-x64 master (2000ms) 91.0 % 83.8 % patched (5000ms) 71.3 % 100 %