atc: fix data race
atc: fix data race

When there are multiple checks, we should be using the argument passed
into the go routine for each check.

[#5575]

Signed-off-by: Clara Fu <d5c8bdbc15689555c92563892e959c79b3fc425f@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse