Don't leave dangling pointers in the GcalEvent cache

The cache has an unowned pointer to the GcalEvent's UID. We need to
update the cache with the GcalEvent's new UID to avoid use-after-free.

Fixes #434
3 jobs for mcatanzaro/#434 in 7 minutes and 54 seconds (queued for 1 second)
Status Job ID Name Coverage
  Flatpak
passed #404448
flatpak

00:07:25

 
  Review
passed #404449
review

00:00:29

manual #404450
allowed to fail manual
stop_review