Bug 32820: Fix cataloguing/value_builder/stocknumberAV.pl

Bug 32820: Fix cataloguing/value_builder/stocknumberAV.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 9a672aed3d45b3741169565b17432e42c962c7d3)
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
(cherry picked from commit f121caf3a3300e6f9e4ee5dc47c5129133e8a6a4)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit ec7535a14f23b50b69914b6c14e95f5cbdb77dd8)
Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>