Remove x86 Mac from non-GPL FFmpeg builds (#207)

Author: scotts

.github/workflows/build_ffmpeg.yaml

@@ -46,7 +46,7 @@ jobs:
       fail-fast: false
       matrix:
         ffmpeg-version: ["4.4.4", "5.1.4", "6.1.1", "7.0.1"]
-        runner: ["macos-m1-stable", "macos-12"]
+        runner: ["macos-m1-stable"]
     uses: pytorch/test-infra/.github/workflows/macos_job.yml@main
     with:
       job-name: Build