snap: Unbreak docker install

It appears that _either_ the GitHub workflow runners have changed their
environment, or the Ubuntu archive has changed package dependencies,
resulting in the following error when building the snap:

```
Installing build dependencies: bc bison build-essential cpio curl docker.io ...

    :

The following packages have unmet dependencies:
docker.io : Depends: containerd (>= 1.2.6-0ubuntu1~)
E: Unable to correct problems, you have held broken packages.
```

This PR uses the simplest solution: install the `containerd` and `runc`
packages. However, we might want to investigate alternative solutions in
the future given that the docker and containerd packages seem to have
gone wild in the Ubuntu GitHub workflow runner environment. If you
include the official docker repo (which the snap uses), a _subset_ of
the related packages is now:

- `containerd`
- `containerd.io`
- `docker-ce`
- `docker.io`
- `moby-containerd`
- `moby-engine`
- `moby-runc`
- `runc`

Fixes: #5545.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

snap/snapcraft.yaml

@@ -89,9 +89,11 @@ parts:
       - -*
     build-packages:
       - ca-certificates
+      - containerd
       - curl
       - gnupg
       - lsb-release
+      - runc
     override-build: |
       source "${SNAPCRAFT_PROJECT_DIR}/snap/local/snap-common.sh"