sync: TestWaitGroupMisuse2 is flaky [1.17 backport]

[gopherbot]

@dmitshur requested issue #38163 to be considered for backport to the next 1.17 minor release.

@gopherbot Please backport to Go 1.17 as a test-only fix. The TestWaitGroupMisuse2 test had a flaky failure during the 1.17.9 release, which requires tests to be re-run and slows the process down.

[gopherbot]

Change https://go.dev/cl/399821 mentions this issue: [release-branch.go1.17] sync: remove TestWaitGroupMisuse2 and TestWaitGroupMisuse3

[gopherbot]

Closed by merging 0fdca72 to release-branch.go1.17.