build job does not work when upstream project has a file called "build"

Hello. The following packages can't use the default salsa-ci.yml because they have a file called "build" in the top-level directory:

• nncp
• simrisc
• yggdrasil

As an example, see this fork of yggdrasil (which has a low build time), where I added a commit to a wip branch with the standard debian/salsa-ci.yml:

https://salsa.debian.org/sanvila/yggdrasil/-/pipelines

The build fails in this way:

$ mkdir -vp ${BUILD_DIR}
mkdir: cannot create directory '/builds/sanvila/yggdrasil/build/': File exists

I suppose this could be solved easily by using a less conventional value for BUILD_DIR.

Thanks.