tls: Cast argument to gcr_simple_certificate_new to avoid compiler warning
tls: Cast argument to gcr_simple_certificate_new to avoid compiler warning

Gcr correctly treats these as unsigned.

GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets