ci: Bump the warning-level

With the previous fixes, we can now build with an increased warning
level to catch more errors. Unfortunately we cannot use the highest
level, as the platform itself relies on some features that -Wpedantic
complains about.

!99
5 jobs for !99 with wip/fmuellner/more-warnings in 7 minutes and 33 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Commit Check
passed #242865
check_commit_log

00:00:20

 
  Source Check
passed #242866
eslint

00:00:37

 
  Build
passed #242867
flatpak

00:05:52

 
  Review
passed #242868
review

00:00:22

passed #242869
allowed to fail manual
stop_review

00:00:19