Use kernel.org mirror for debootstrap

Turns out, the internal GCE mirror is designed only for actual vms
running in GCP, and either didn't play well with the Concourse
container's egress or doesn't server jammy.

Fixes

debootstrap --arch=amd64 jammy /mnt/stemcells/null/null/ubuntu/work/work/chroot http://gce.archive.ubuntu.com/ubuntu
I: Retrieving InRelease
I: Retrieving Release
E: Failed getting release file http://gce.archive.ubuntu.com/ubuntu/dists/jammy/Release

Author: selzoc

ci/pipelines/builder.yml

@@ -248,7 +248,7 @@ jobs:
     params:
       OPERATING_SYSTEM_NAME: ubuntu
       OPERATING_SYSTEM_VERSION: (@= data.values.stemcell_details.os_short_name @)
-      UBUNTU_DEBOOTSTRAP_MIRROR: http://gce.archive.ubuntu.com/ubuntu #! Ubuntu's GCP-internal mirror, must change if we change Concourse IaaS!
+      UBUNTU_DEBOOTSTRAP_MIRROR: http://mirrors.edge.kernel.org/ubuntu
     privileged: true
     vars:
       image_os_tag: (@= data.values.stemcell_details.os_short_name @)