Make timezone field optional in personal event mutations

added part::backend type::bug labels

assigned to @yuha

added core-4.0 label

created branch 1104-make-timezone-field-optional-in-personal-event-mutations to address this issue

mentioned in merge request !1694 (merged)

assigned to @permcu and unassigned @yuha

mentioned in commit 1cc55b52

closed with merge request !1694 (merged)

changed milestone to /AlekSIS%"[NLnet #6 (closed)] Do integration/final tests with pilot schools"