CI: add Ubuntu 24.04 into the mix

The release have been out for a bit over a month now. At the same time,
23.10 has another month or so remaining and 18.04 is an extended LTS.

We can re-evaluate if we want to drop those at later point - for now
they just work and are supported, so keep them.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

.github/workflows/tests.yml

@@ -37,6 +37,7 @@ jobs:
           - {name: "gentoo/stage3", tag: "latest"}
           - {name: "opensuse/tumbleweed", tag: "latest", variant: "-default", url: "registry.opensuse.org/"}
           - {name: "opensuse/leap", tag: "15.5", variant: "-default", url: "registry.opensuse.org/"}
+          - {name: "ubuntu", tag: "24.04"}
           - {name: "ubuntu", tag: "23.10"}
           - {name: "ubuntu", tag: "22.04"}
           - {name: "ubuntu", tag: "20.04"}