graphics/qgis-ltr: Update to 3.10.11

Changelog[1]:
Bugfix release with many fixes and some minor enhancements,
like adding default UTF-8 encoding to grass provider by default.

[1] https://github.com/qgis/QGIS/compare/final-3_10_10...final-3_10_11

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D27079