databases/mdbx: Update 0.13.11 => 0.13.12
Changelog:
https://sourcecraft.dev/dqdkfa/libmdbx/browse/ChangeLog.md?rev=tag%3Av0.13.12
PR: 295340
Sponsored by: UNIS Labs
MFH: 2026Q2
(cherry picked from commit e1f2ef9c22b8f56d8bbc2435f4f00293263aaf6b)