Fix maven-releng Docker image
After a rebuild of the Docker image, the build fails with the following error message:
[...]
Getting source from Git repository 00:01
Fetching changes...
Reinitialized existing Git repository in /builds/af3/maven-releng/.git/
Checking out dd44067d as master...
Skipping Git submodules setup
Executing "step_script" stage of the job script 00:01
Using docker image sha256:256bcebbbfb812e50d66017e5d228de1d526d1779fcb61420db68cd65bd1e160 for git.fortiss.org:5001/af3/maven-releng:latest with digest git.fortiss.org:5001/af3/maven-releng@sha256:4f1a6d5300905b37022c2027d37a3916d3e3c21ace14bf31dc6dddc80c9641f9 ...
shell not found
Cleaning up project directory and file based variables 00:00
ERROR: Job failed: exit code 1