Track ubuntu-latest where relevant and possible.
We can't update to ubuntu-latest when building and running BPF
selftests, though, because our QEMU image has too old of an GLIBC.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
The current version of actions/checkout is v3. That means that v2, which
we currently use, has been superseded. Update the version we use
accordingly.
Signed-off-by: Daniel Müller <deso@posteo.net>