flatpak: Use pinned Grilo

Master is broken at the moment, use a known working Grilo to keep the nightlies
working.

See grilo!42.
4 jobs for wip/mschraal/flatpak-pin-grilo-0.3.8 in 8 minutes and 10 seconds (queued for 1 second)
Status Job ID Name Coverage
  Check
passed #357425
flake8

00:01:18

 
  Build Flatpak
passed #357426
flatpak

00:05:17

 
  Deploy
passed #357427
review

00:00:31

passed #357428
allowed to fail manual
stop_review

00:01:03