Bug 32212: (bug 32030 follow-up) Restore bootstrap 4

Bug 32212: (bug 32030 follow-up) Restore bootstrap 4

During the development of the eRM module I've tried to use bootstrap 5
(and vue-bootstrap), but I didn't manage to make it work without
modifying the version used in Koha. This change is actually not needed
and we can keep version 4.
See commit 8c32f186d5a62e742621c35cfacff5b22bb42b71
Bug 32030: ERM - Remove BootstrapVue3

Test plan:
% yarn install
% git diff
you should notice the version change in yarn.lock

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>