[Qa-jenkins-scm] race condition found

[jenkins at jenkins.debian.net]

Warning, package libipc-shareable-perl in testing on amd64 is probably already building elsewhere, exiting.
Please check https://jenkins.debian.net/job/reproducible_builder_alpha/42487/ and https://reproducible.debian.net/testing/amd64/libipc-shareable-perl for a different build.
The race condition was cought while writing the lockfile.