x11-wm/river: update 0.3.11 -> 0.3.12
Changelog: https://codeberg.org/river/river/releases/tag/v0.3.12
Major changes:
- updates the required Zig version to 0.15
Reorder Makefile to make portlint happy
PR: 289011
Reported by: Pero Oršolić <bsd@orsolic.org>