x11-wm/picom: Improve "disable git" patch
Make it ready for upstream:
https://github.com/yshui/picom/pull/1520
While here remove unnecessary GH_PROJECT - it have default value.
PR: 295255
Approved by: José Maldonado <yukiteruamano@volfread.xyz> (maintainer, timeout 2 weeks)
Sponsored by: UNIS Labs
MFH: 2026Q2
(cherry picked from commit 166cb5a5a5a8c662b88b6b356cc5bb057ee5968d)