Bug 25514: Try to fix random failure from REST/Plugin/Objects.t

Bug 25514: Try to fix random failure from REST/Plugin/Objects.t

It's causing a "Premature connection close" error

https://docs.mojolicious.org/Mojolicious/Guides/FAQ#What-does-Premature-connection-close-mean

This is just a guess but maybe it would help to have the Test::Mojo
object initiated just before the get?

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 926ad3c1a69074b2905d9ef03e639db6ba8d6865)

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>