force_exit() to make exit work with all `fdroid build` conditions

The build command has to use some threading stuff to handle the timeout and
locks.  This seems to prevent the command from exiting, unless this hack is
used.
3 jobs for force_exit in 19 minutes and 32 seconds
Status Job ID Name Coverage
  Test
passed #120401881
lint_format_safety_bandit_checks

00:02:59

passed #120401880
metadata_v0

00:03:51

passed #120401877
test

00:19:32