We only support the two most recent minor releases.

Refs CVE-2022-28948

Mark `VerifyNone(...)` as a test `Helper` function, so that it reports the error at the call site, rather than `leaks.go:78:`.

From the [go docs](https://pkg.go.dev/testing#T.Helper):

> Helper marks the calling function as a test helper function. When printing file and line information, that function will be skipped. Helper may be called simultaneously from multiple goroutines.

This is useful for tests that verify go routines at multiple points, so failures can be more easily distinguished.

This adds Cleanup option which can be passed to VerifyTestMain and
VerifyNone. This takes in a function that will be executed at the
end of the leak verification.

Internal Ref: GO-888
Fix #63

Co-authored-by: Abhinav Gupta <[email protected]>
Co-authored-by: Abhinav Gupta <[email protected]>

This updates testify dependency to v1.8.0 (most recent version) and
cleans up some tests using new APIs.

Co-authored-by: Abhinav Gupta <[email protected]>