Github webhooks ignore disable flag for concurrent build

[ghost]

I have a docker-compose build type that fails when two builds are simultaneously running on the same box. The PR was created from a branch in the same repo. So additional push of a commit resulted in github webhook firing the DotCi project for both the branch and the PR.

Typically this would not be a problem since COMPOSE_PROJECT_NAME is unique by including BUILD_NUMBER. However this project is currently hardcoded to use the same docker image name per https://github.com/jenkinsci/docker/blob/2.0-previews/tests/tests.bats#L3-L4

The point is that /configure to disable "Execute concurrent builds if necessary" is not respected. So is it possible that DotCi instance ignoring this flag.