Bug 32823: Fix cataloguing/value_builder/unimarc_field_100_authorities.pl

Bug 32823: Fix cataloguing/value_builder/unimarc_field_100_authorities.pl

Use event parameter

This is part of the refactoring happening in bug 30975

Test plan:
1. Verify that the plugin continues to work as before

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 19c26fcc5a5ae72a2d6cd85d6586b82b154cbd08)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>