databases/py-pglast: Update to 1.2

Changelog:

• Implement new split() function
• Implement BooleanTest printer

https://github.com/lelit/pglast/blob/v1.2/CHANGES.rst

PR: 236338
Submitted by: Jaroslaw Zurek <j.zurek@fudosecurity.com>
Approved by: tcberner (mentor), maintainer
Differential Revision: https://reviews.freebsd.org/D19522