Substitutions: Empty teacher drop-down

Steps to reproduce:

• Go to: Timetables -> Daily lessons -> {random lesson} -> Substitution

• Click on "Teachers"

Expected: List of teachers opens

Actual result: Nothing happens

changed due date to April 23, 2022

added prio::1 type::bug labels

assigned to @yuha

created branch 173-substitutions-empty-teacher-drop-down to address this issue

mentioned in merge request !260 (merged)

closed with merge request !260 (merged)

mentioned in commit 735421b5