fix(ci): bump DemoPlayerMac FFmpegBuild pin to c07f908 (avfilter/zimg)

The 2.1.1 release-dmg build failed: AetherEngine 2.1.1 imports Libavfilter,
but DemoPlayerMac's locked Package.resolved still pinned FFmpegBuild at
1a28db3 (pre-avfilter), so the module wasn't found. Advance the pin to the
avfilter+zimg build. Verified: swift build of DemoPlayerMac succeeds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: superuser404notfound