runtime/pprof: TestMorestack failures on darwin/arm64

[bcmills]

2021-06-15T10:13:08-abc56fd/darwin-arm64-11_0-toothrot
2021-04-30T00:32:42-303b194/darwin-arm64-11_0-toothrot

See previously #44418 (CC @cherrymui).

[bcmills]

Marking as release-blocker for 1.17 because the tests are newly unskipped on Darwin as of CL 292229 (CC @golang/release).

If it isn't important that the tests pass on this platform for 1.17, it seems ok to unblock the release by adding a skip on this builder platform (GOOS + GOARCH), although fixing the test would be better still.

[prattmic]

Perhaps we just need to increase the stack growth time even more than http://golang.org/cl/307730?

[cherrymui]

Yeah, probably. Changed copying size from 8<<16 to 8<<18, it seems to pass on my Apple M1 machine reliably with 1000 runs. I'll send a CL.

[gopherbot]

Change https://golang.org/cl/329869 mentions this issue: runtime/pprof: deflake TestMorestack more