phases: emit phases to pushkey protocol in deterministic order

An upcoming test will report exact bytes sent over the wire protocol.
Without this change, the ordering of phases listkey data is
non-deterministic.

mercurial/phases.py

@@ -116,6 +116,7 b' from . import ('
     error,
     smartset,
     txnutil,
+    util,
 )
 
 allphases = public, draft, secret = range(3)
@@ -386,7 +387,8 b' def retractboundary(repo, tr, targetphas'
 
 def listphases(repo):
     """List phases root for serialization over pushkey"""
-    keys = {}
+    # Use ordered dictionary so behavior is deterministic.
+    keys = util.sortdict()
     value = '%i' % draft
     for root in repo._phasecache.phaseroots[draft]:
         keys[hex(root)] = value