Bug 24000: Some modules do not return 1

Bug 24000: Some modules do not return 1

This patch adds "1;" to the end of the following perl files:
Koha/Filter/MARC/EmbedItemsAvailability.pm
Koha/Filter/MARC/EmbedSeeFromHeadings.pm
Koha/Filter/MARC/Null.pm
Koha/Item/Search/Field.pm
Koha/SearchEngine.pm
misc/translator/VerboseWarnings.pm
t/lib/Koha/Plugin/Test.pm

This indicates the succesful execution of the initialization code.

Test plan:
Ensure that there are no other perl files that need "1;", but dont have
it.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>