Fix bug in a parallel test (#299)
Fix bug in a parallel test (#299)

There was a bug in the Dig.As error cases test which was using
t.Parallel to run the tests in parallel. But it was doing that using
a loop iterator, so tt was being changed during test execution.

Note this manifests in a quite cryptic way - codecov complained some
lines were not being covered, even though tests explicitly used those
cases.
uber-go/dig,uber-go/dig