net-im/py-matrix-synapse: Update to 1.25.0

Several features are deprecated now, which means:

• Last release which guarantees support for Python 3.5
• Support for PostgreSQL 9.5 will end early in February 2021
• Support for Python 3.6 and PostgreSQL 9.6 will end near the end of 2021

Changelog: https://github.com/matrix-org/synapse/releases/tag/v1.25.0

PR: 252912
Submitted by: Sascha Biberhofer <ports@skyforge.at> (maintainer)
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D28298