rust-filepatterns: fix type of warnings tuple to (bytes, bytes)
Otherwise warn() in match.py would fail if the warning contains non-ASCII
character.
We might want to add a thin ByteString wrapper around Vec<u8> to
implement ToPyObject<ObjectType = PyBytes>, but I'm not sure.
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..