Fix the openlinks test by properly converting gunicode to gchar
Ubuntu s390x build log example https://launchpadlibrarian.net/588175976/buildlog_ubuntu-jammy-s390x.gedit_41.0-2_BUILDING.txt.gz
ERROR:../plugins/openlinks/unit-tests/test-open-links.c:54:test_uri_detection: 'is_uri' should be TRUE
The casting of a gunicode to a gchar the way it's currently done seems wrong, the proposed change should fix the issue