graphics/qgis-ltr: Update to 3.16.13

A critical issue occurs in QGIS 3.16.12 that can cause plugins to hang (mainly on Windows, but also in some Unix-like systems under certain circumstances).
Users of the LTR version 3.16.12 are encouraged to upgrade to 3.16.13 [1]

[1] https://blog.qgis.org/2021/11/06/psa-update-to-3-16-13/