This is because Pg 9.6's unaccent() function was corrected so that unaccent('Œuvres') will now return 'OEuvres'.
The test case is easy enough to adjust, but it's probably worth poking at this a bit more to identify other cases where the normalization changed, as some REINDEXes on columns in actor.usr may be called for if patron names contain any of the affected ligatures.
The following test in t/lp1501781- unaccent_ and_squash. pg will fail to pass when running on PostgreSQL 9.6:
SELECT is(evergreen. unaccent_ and_squash( 'Œuvres' ),
'euvres', 'oe ligature');
This is because Pg 9.6's unaccent() function was corrected so that unaccent('Œuvres') will now return 'OEuvres'.
The test case is easy enough to adjust, but it's probably worth poking at this a bit more to identify other cases where the normalization changed, as some REINDEXes on columns in actor.usr may be called for if patron names contain any of the affected ligatures.
Evergreen master