Bug 41901: (follow-up) Fix perlcritic violation in unit tests

Remove explicit "return undef" in favour of bare "return" to
satisfy Perl::Critic (PBP p.199).

Signed-off-by: Brian J. Barr <brian.barr@churchofjesuschrist.org>
Signed-off-by: Andrew Fuerste Henry <andrew@bywatersolutions.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

t/db_dependent/api/v1/authorities.t

@@ -180,7 +180,7 @@ subtest 'post() tests' => sub {
         'fetch',
         sub {
             my ( $class, $id ) = @_;
-            return undef if $id == 999999;
+            return if $id == 999999;
             my $rt      = ( $id == 42 ) ? 'biblio' : 'authority';
             my @matches = ();
             @matches = (