The issue is related to a security update of git on Ubuntu 20.04. It has been announced 12 april 2022 (Git security vulnerability announced - The GitHub Blog). A new configuration parameter has been introduced (from Git - git-config Documentation) :
safe.directoryThese config entries specify Git-tracked directories that are considered safe even if they are owned by someone other than the current user. By default, Git will refuse to even parse a Git config of a repository owned by someone else, let alone run its hooks, and this config setting allows users to specify exceptions, e.g. for intentionally shared repositories (see the
--sharedoption in git-init[1]).This is a multi-valued setting, i.e. you can add more than one directory via
git config --add. To reset the list of safe directories (e.g. to override any such directories specified in the system config), add asafe.directoryentry with an empty value.This config setting is only respected when specified in a system or global config, not when it is specified in a repository config or via the command line option
-c safe.directory=<path>.The value of this setting is interpolated, i.e.
~/<path>expands to a path relative to the home directory and%(prefix)/<path>expands to a path relative to Git’s (runtime) prefix.
For me the issue is solved adding
sudo git config --global --add safe.directory /home/user/darktable/master
before
sudo cmake --build "/home/user/darktable/master/build" --target install -- -j12
where /home/user/darktable/master is the location of the git clone of darktable master.