[Qa-jenkins-scm] race condition found

[jenkins at jenkins.debian.net]

Warning, package haskell-wai-conduit in experimental on amd64 is probably already building elsewhere, exiting.
Please check https://jenkins.debian.net/job/reproducible_builder_delta/6454/ and https://reproducible.debian.net/experimental/amd64/haskell-wai-conduit for a different build.
The race condition was cought while writing the lockfile.