phabricator: convert phabhunk and phabchange keys to bytes when finalising

I thought I had included this code already but I'd missed it out.  One of the
disadvantages of attrs is that all the keys are unicode strings on py3, but we
need them to be byte strings.

Differential Revision: https://phab.mercurial-scm.org/D7066

hgext/phabricator.py

@@ -518,7 +518,7 b' class phabchange(object):'
     def addhunk(self, hunk):
         if not isinstance(hunk, phabhunk):
             raise error.Abort(b'phabchange.addhunk only takes phabhunks')
-        self.hunks.append(hunk)
+        self.hunks.append(pycompat.byteskwargs(attr.asdict(hunk)))
         # It's useful to include these stats since the Phab web UI shows them,
         # and uses them to estimate how large a change a Revision is. Also used
         # in email subjects for the [+++--] bit.
@@ -549,7 +549,9 b' class phabdiff(object):'
     def addchange(self, change):
         if not isinstance(change, phabchange):
             raise error.Abort(b'phabdiff.addchange only takes phabchanges')
-        self.changes[change.currentPath] = change
+        self.changes[change.currentPath] = pycompat.byteskwargs(
+            attr.asdict(change)
+        )
 
 
 def maketext(pchange, ctx, fname):