Bug 32853: Fix cataloguing/value_builder/unimarc_field_125.pl

Bug 32853: Fix cataloguing/value_builder/unimarc_field_125.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: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 826aeaf22f36fb3ebacafdacf7c270cc72d8c5fe)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit dd34d7df04c8674cf32cf8d7daa001d773213535)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>