Permissions for /dev/loop needed. Mounting filesystems

I would like to automate our current process with gitea actions.
Currently we’re have a script we trigger manually, which runs in a dedicated VM to create some filesystem-images. For this we create a local img-file and then we use tools like kpartx&Co to mkfs and mount it via loopback… and umount after finish …

Currently we’re using the DinD-Runner which works so far perfect for building containers, but it seems the started containers for the jobs don’t have the permissions to access /dev/loop.

While reading the docs I didn’t find a way to add additional parameters or options to the spawned job-containers. What am I missing?