Bug 28288: Prevent XSISBN.t to fail if service is returning 500

16:00:45 koha_1       | WARNING: URL Request Failed 500 read timeout
16:00:45 koha_1       | WARNING: URL Request Failed 500 read timeout
16:00:45 koha_1       | WARNING: URL Request Failed 500 Can't connect to www.librarything.com:443
16:00:45 koha_1       | # Looks like you planned 6 tests but ran 5.
16:00:45 koha_1       | [13:59:51] t/db_dependent/XISBN.t
16:00:45 koha_1       | Dubious, test returned 255 (wstat 65280, 0xff00)
16:00:45 koha_1       | Failed 1/6 subtests
16:00:45 koha_1       | 	(less 3 skipped subtests: 2 okay)

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

t/db_dependent/XISBN.t

@@ -60,7 +60,7 @@ t::lib::Mocks::mock_preference( 'ThingISBN', 1 );
 my $results_thingisbn;
 eval { $results_thingisbn = C4::XISBN::get_xisbns($isbn1, $biblionumber4); };
 SKIP: {
-    skip "Problem retrieving ThingISBN", 1
+    skip "Problem retrieving ThingISBN", 2
         unless $@ eq '';
     ok( (any { $_->{'biblionumber'} eq $biblionumber1 } @$results_thingisbn),
         "Gets correct biblionumber from a book with a similar isbn using ThingISBN." );