net/http: TestTimeoutHandlerAndFlusher flaky on darwin-arm64-corellium [1.13 backport]

[gopherbot]

@bcmills requested issue #34573 to be considered for backport to the next 1.13 minor release.

@gopherbot, please backport to Go 1.13: the flaky test was also backported.

[gopherbot]

Change https://golang.org/cl/197719 mentions this issue: [release-branch.go1.13] net/http: remove TestTimeoutHandlerAndFlusher due to flakes

[gopherbot]

Closed by merging 0c07603 to release-branch.go1.13.