debug-discovery: do not abort on unrelated repositories

This is a useful case to consider, so we should not abort in this case.
A warning is still issued.

mercurial/debugcommands.py

@@ -1302,7 +1302,12 b' def debugdiscovery(ui, repo, remoteurl=b'
                 revs = logcmdutil.revrange(repo, pushedrevs)
                 nodes = [repo[r].node() for r in revs]
             common, any, hds = setdiscovery.findcommonheads(
-                ui, repo, remote, ancestorsof=nodes, audit=data
+                ui,
+                repo,
+                remote,
+                ancestorsof=nodes,
+                audit=data,
+                abortwhenunrelated=False,
             )
             return common, hds