Update expected Pillow 10 release date: 2023-07-01

[hugovk]

Python now has an annual release cadence in October, but the EOL dates haven't yet synced up: Python 3.7 will be the last (EOL: 2023-06-27) until they're also aligned to October.

cycle	latest	release	eol
3.10	3.10.0	2021-10-04	2026-10-04
3.9	3.9.7	2020-10-05	2025-10-05
3.8	3.8.12	2019-10-14	2024-10-14
3.7	3.7.12	2018-06-27	2023-06-27
3.6	3.6.15	2016-12-23	2021-12-23

https://endoflife.date/python

That means if we tie the major bump Pillow 9->10 to the Python 3.7 drop (not guaranteed but most likely), then that will be in the 2023 Q3 release, not 2023 Q1.

And so we have until 2022-07-01 to deprecate new things, for them to have 12 months of deprecation before removal in Pillow 10.