test: use ADD for ejabberd test

[crazy-max]

relates to https://github.com/tonistiigi/binfmt/actions/runs/12197461179/job/34027180497#step:6:163

 > [5/5] RUN git clone https://github.com/processone/ejabberd.git .     && git checkout 99d9e315a3c0524d84197e63741790d5893c51f4     && mv .github/container/ejabberdctl.template .     && ./autogen.sh     && ./configure --with-rebar=mix     && make deps     && make rel:
19.34   git switch -c <new-branch-name>
19.34 
19.34 Or undo this operation with:
19.34 
19.34   git switch -
19.34 
19.34 Turn off this advice by setting config variable advice.detachedHead to false
19.34 
19.34 HEAD is now at 99d9e315a Don't set affiliation to 'none' if it's already 'none' in mod_muc_room:process_item_change/3
19.36 Error while loading /ejabberd/./autogen.sh: Exec format error