gitlab-ci/leak-sanitizer.supp: Suppress entire libfontconfig

As we can't really use `cleanup_after_cairo()` in our headless backend,
add more leak suppression entry, found while running the entire
test suite.

FcConfigSubstituteWithPat was already added (which seems to be main
source) but found a couple of more while running the entire suite.

The issue is that we need to set fast unwind to zero in order track
those leaks but that would result into some massive runtime penalty and
we get into the issue of timing out some of the tests.

So rather than doing that, just add the entire libconfig library and be
done with it. With it, this removes any pango/cairo former symbols as
that seems to catch all other leaks as well.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>