update ffmpeg workflow

Author: NullPointerException

.github/workflows/build-ffmpeg.yml

@@ -52,7 +52,7 @@ jobs:
           ./android.sh ${BUILD_OPTIONS}
 
       - name: 上传 LTS AAR 文件
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: ffmpeg-kit-android-lts-aar
           path: bundle-android-aar-lts/*.aar