textproc/py-mkdocs-material: Update to 9.7.7

• Also add a DEPRECATED note, but don't set an EXPIRATION_DATE yet, because the port is currently still being used by some consumers.

Changelog:

https://github.com/squidfunk/mkdocs-material/releases/tag/9.7.7

MFH: 2026Q3
Security: 1976b049-8ccc-11f1-b333-901b0edee044
(cherry picked from commit c0439516cef7ae3e60d7e10b3af4d2838016aafd)