PostBuild Matrix Update

Build Matrix Update CI now covers Pixel 6 through 11 only. Older devices (Pixel 1–5a) were skipped because their OTAs lack the modern partition layout (product, system_ext, init_boot, etc.) that our extraction pipeline expects — the script simply fails on them. Plus, Google stopped shipping updates for those years ago, so their build.prop values are already final. Weekly rebuilds would just produce the same props over and over. Previous releases for older devices are still up if you need them.