Increase golangci-lint timeout to 20m
I've seen this now sporadically happen in a few pipeline runs in different branches:
- https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/jobs/4299237569#L33
- https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/jobs/4298377943#L33
So lets increase is from the default 1m to 5m.