System test Docker container for Ubuntu 24.04 fails in groupadd

[MakisH]

Running the system tests locally using PLATFORM:ubuntu2404 fails with:

#6 [prepare base_image 2/2] RUN groupadd -g 1000 precice && useradd -u 1000 -g 1000 -ms /bin/bash precice
#6 0.243 groupadd: GID '1000' already exists
#6 ERROR: process "/bin/bash -c groupadd -g ${PRECICE_GID} precice && useradd -u ${PRECICE_UID} -g ${PRECICE_GID} -ms /bin/bash precice" did not complete successfully: exit code: 4
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 > [fluid-openfoam base_image 2/2] RUN groupadd -g 1000 precice && useradd -u 1000 -g 1000 -ms /bin/bash precice:
0.243 groupadd: GID '1000' already exists

This is not the case on Ubuntu 22.04.

Also reported in #731 (comment)