evolve: mark new hash-salting extras keys as uninteresting for effect flag
The user doesn't care if the
`evolve_source_local`/`evolve_source_other` values in the extras
changed, so this patch adds them to the blacklist that already exists
for that purpose.
This should also fix the flakiness we've seen in some tests. The
flakiness seemed to stem from `mercurial.obsutil.geteffectflag()` not
sorting extras keys. That means we ran into it relatively often for
the `evolve_source_local`/`evolve_source_other` keys because there
were two of them. That sorting bug should be fixed upstream.