don't create mp3 folder

.github/workflows/videobuild.yml

@@ -26,7 +26,7 @@ jobs:
           sudo apt install -y sox libsox-fmt-mp3 ffmpeg
           pip install requests sox b2sdk
           npm install puppeteer
-          mkdir json thumbnails frames mp3
+          mkdir json thumbnails frames
       - name: Python preprocessing
         run: |
           python preprocess.py https://www.oyez.org/cases/2023/22-340