[Qa-jenkins-scm] race condition found

[jenkins at jenkins.debian.net]

Warning, package php-horde-tree in testing on amd64 is probably already building elsewhere, exiting.
Please check https://jenkins.debian.net/job/reproducible_builder_zeta/8749/ and https://reproducible.debian.net/testing/amd64/php-horde-tree for a different build.
The race condition was caught while marking the build attempt in the database.