Avoid `runtime-spec` upgrade until containerd supports it

[FedeDP]

Bumping github.com/opencontainers/runtime-spec to v1.3.0 means that any project using tetragon packages, and having a dep on containerd would fail to build, since containerd still uses github.com/opencontainers/runtime-spec@v1.2.1.
The new runtime-spec uses a pointer for LinuxPids::Limit : opencontainers/runtime-spec@869b2d5#diff-9790b3b8b39fc583eab8f6d97ac27ae3f35dbe339000c746faf64615125a8ec7L435-L438, while containerd still uses a non-pointer type: https://github.com/containerd/containerd/blob/main/pkg/oci/spec_opts.go#L1604

We will be able to finally bump it once containerd will be ported to v.1.3.0.

See #4335.

[FedeDP]

containerd/containerd#12465 will eventually allow us to bump the deps.

[FedeDP]

Update: the aforementioned PR has been merged. We just need to wait for a containerd tag now. Hopefully it will come soon.