don't isntall pngquant

Author: Joon-Klaps

.github/workflows/build-docs.yml

@@ -35,7 +35,6 @@ jobs:
           path: .cache
           restore-keys: |
             mkdocs-material-
-      - run: apt-get install pngquant
       - name: Install dependencies
         run: pip install mkdocs-material pymdown-extensions pillow cairosvg mike
       - name: Build docs