Fix flatpak CI job and minor cleanups
Seems the overriden XDG_CONFIG_HOME was propagated to the flatpak runner (even though it's only defined for the test suite) which made CI jobs fail with permission denied errors.
Seems the overriden XDG_CONFIG_HOME was propagated to the flatpak runner (even though it's only defined for the test suite) which made CI jobs fail with permission denied errors.