Otherwise this can trigger test failures. Similar to what we
did in libhandy.
Fixes errors like:
---
G_DEBUG='gc-friendly,fatal-warnings' G_TEST_BUILDDIR='/home/purism/builds/calls/_build/tests' PYTHONDONTWRITEBYTECODE='yes' MALLOC_CHECK_='2' GSETTINGS_BACKEND='memory' G_TEST_SRCDIR='/home/purism/builds/calls/tests' /home/purism/builds/calls/_build/tests/manager
--- stderr ---
(/home/purism/builds/calls/_build/tests/manager:10212): dbind-WARNING **: 12:01:50.237: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files
-------
c3e6a444db