tf-stage1: Increase mirror.pkgbuild.com disk size

Repos are growing and we were getting notifications about 91% utilization. That's a bit close IMO and we should just make sure to increase it to be outside of our own thresholds.

requested review from @gromit

assigned to @svenstaro

approved this merge request

This is now deployed. I also ran btrfs fi resize max /srv/ftp

Looks good:

[root@mirror ~]# df -h | grep ftp
/dev/sdb        150G  113G   37G  76% /srv/ftp

merged manually