CI: run `make clean` before `make docker-all`
CI: run `make clean` before `make docker-all`

make's modify-time build caching system causes rebuilds to be skipped on
a freshly-cloned repo, since build output is part of the repo itself.

This doesn't result in a diff where a diff would normally be expected.

Signed-off-by: Timo Beckers <98c2d5a1e48c998bd9ba9dbc53d6857beae1c9bd@isovalent.com>

cilium/ebpf,cilium/ebpf