contrib/backporting: Include golang in the image
contrib/backporting: Include golang in the image

Dev doctor is written with Go and is unable to be used in
the container right now:
```
❮ docker run -e GITHUB_TOKEN -v $(pwd):/cilium -v "$HOME/.ssh":/home/user/.ssh \
      -it cilium-backport /bin/bash
$ go run ./tools/dev-doctor --backporting
bash: go: command not found
```

Signed-off-by: Glib Smaga <e6fb06210fafc02fd7479ddbed2d042cc3a5155e@gsmaga.com>

michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium