patch: fix header.__repr__() to not have `b''` prefixes in file names

Spotted by Denis Laxalde.

Differential Revision: https://phab.mercurial-scm.org/D7695

mercurial/patch.py

@@ -963,7 +963,9 b' class header(object):'
         return self.files()[-1]
 
     def __repr__(self):
-        return '<header %s>' % (' '.join(map(repr, self.files())))
+        return '<header %s>' % (
+            ' '.join(pycompat.rapply(pycompat.fsdecode, self.files()))
+        )
 
     def isnewfile(self):
         return any(self.newfile_re.match(h) for h in self.header)