Bump minimum glib version to v2.66

Bump minimum glib version to v2.66

Now that we dropped support for CentOS 8 and Ubuntu 20.04, we can
look into bumping the glib version to a new minimum for further
clean-ups. According to repology.org, available versions are:

 CentOS Stream 9:       2.66.7
 Debian 11:             2.66.8
 Fedora 38:             2.74.1
 Freebsd:               2.78.4
 Homebrew:              2.80.0
 Openbsd:               2.78.4
 OpenSuse leap 15.5:    2.70.5
 pkgsrc_current:        2.78.4
 Ubuntu 22.04:          2.72.1

Thus it should be safe to bump the minimum glib version to 2.66 now.
Version 2.66 comes with new functions for URI parsing which will
allow further clean-ups in the following patches.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20240418101056.302103-8-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>