convert: use the new 'phase.registernew' function

hgext/convert/hg.py

@@ -345,7 +345,7 b' class mercurial_sink(common.converter_si'
                 if commit.rev != node:
                     ctx = self.repo[node]
                     if ctx.phase() < phases.draft:
-                        phases.retractboundary(self.repo, tr, phases.draft,
+                        phases.registernew(self.repo, tr, phases.draft,
                                                [ctx.node()])
 
             text = "(octopus merge fixup)\n"