project.conf .gitlab-ci.yml: switch to Packet cache

Enable "local" cache deployed on one of Packet.net hosts. CAS server
deployed on Ceph storage shows some infrastructure issues we are trying
to sort out.
9 jobs for barthalion/local-cache in 185 minutes and 22 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Track
passed #793782
gnome-build-meta x86_64
track

00:48:12

 
  Build
passed #793785
gnome-build-meta aarch64
build-gnome-core-aarch64

02:17:08

passed #793786
gnome-build-meta armhf
build-gnome-core-arm

00:46:40

passed #793784
gnome-build-meta x86_64
build-gnome-core-i386

00:38:52

passed #793783
gnome-build-meta x86_64
build-gnome-core-x86_64

00:57:36

 
  Image
manual #793788
gnome-build-meta aarch64 allowed to fail manual
pinebook-pro-image
manual #793790
gnome-build-meta aarch64 allowed to fail manual
raspberrypi-4-image
manual #793789
gnome-build-meta aarch64 allowed to fail manual
rock64-image
manual #793787
gnome-build-meta x86_64 allowed to fail manual
vm-image-x86_64