exchange: use '%d' % x instead of str(x) to encode ints

Recommended by Yuya instead of using pycompat.bytestr() in this case.

mercurial/exchange.py

@@ -791,8 +791,8 b' def _pushb2phases(pushop, bundler):'
         part = bundler.newpart('pushkey')
         part.addparam('namespace', enc('phases'))
         part.addparam('key', enc(newremotehead.hex()))
-        part.addparam('old', enc(str(phases.draft)))
-        part.addparam('new', enc(str(phases.public)))
+        part.addparam('old', enc('%d' % phases.draft))
+        part.addparam('new', enc('%d' % phases.public))
         part2node.append((part.id, newremotehead))
         pushop.pkfailcb[part.id] = handlefailure