Update FFmpeg arm64 CI (#3578)

Summary: Pull Request resolved: #3578

Reviewed By: nateanl

Differential Revision: D48971591

Pulled By: mthrok

fbshipit-source-id: a76cf8f1287c076d7b6919d901eda0ce832bdb7d

Author: mthrok

.github/workflows/ffmpeg.yml

@@ -44,8 +44,7 @@ jobs:
       job-name: Build
       upload-artifact: ffmpeg-lgpl
       repository: pytorch/audio
-      runner: "linux.t4g.2xlarge"
-      no-sudo: true
+      runner: linux.arm64.2xlarge
       docker-image: pytorch/manylinuxaarch64-builder:cpu-aarch64
       script: |
         export FFMPEG_VERSION="${{ matrix.ffmpeg_version }}"