pmaports.cfg: set pmbootstrap_min_version=1.53.0 (MR 4472)

Using versions before 1.53.0 leads to various problems, from Alpine
v3.18 not appearing as supported, to some timezone file conflicts that
were fixed long ago. Bump the version to force users to use at least
that version.

pmaports.cfg

 # Reference: https://postmarketos.org/pmaports.cfg
 [pmaports]
 version=7
-pmbootstrap_min_version=1.47.0
+pmbootstrap_min_version=1.53.0
 channel=edge
 supported_root_filesystems=btrfs,ext4,f2fs
 supported_firewall=nftables