obsutil: sort metadata before comparing in geteffectflag()

This is probably less important now that we dropped Python 2. We do still
support Python 3.6 though, and the dictionaries aren't ordered there either
(that was a big change that came with 3.7).

Still, maybe it's a good idea to sort metadata explicitly.

mercurial/obsutil.py

@@ -468,10 +468,10 b' def geteffectflag(source, successors):'
 
         # Check if other meta has changed
         changeextra = changectx.extra().items()
-        ctxmeta = list(filter(metanotblacklisted, changeextra))
+        ctxmeta = sorted(filter(metanotblacklisted, changeextra))
 
         sourceextra = source.extra().items()
-        srcmeta = list(filter(metanotblacklisted, sourceextra))
+        srcmeta = sorted(filter(metanotblacklisted, sourceextra))
 
         if ctxmeta != srcmeta:
             effects |= METACHANGED