gitlab-ci: add cache, extend timeouts/retries to stabilize Fedora job
gitlab-ci: add cache, extend timeouts/retries to stabilize Fedora job

This is happening too often:
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.
Error: Error downloading packages:
  Curl error (28): Timeout was reached for https://mirrors.fedoraproject.org/metalink?repo=updates-released-f29&arch=x86_64 [Connection timed out after 30001 milliseconds]
ERROR: Job failed: exit code 1

https://gitlab.com/fdroid/fdroidserver/-/jobs/152719443

# Conflicts:
#	.gitlab-ci.yml

f-droid/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver