[ci] Try pin awalsh128/cache-apt-pkgs-action

Author: SilverRainZ

.github/workflows/gh-pages.yml

@@ -29,7 +29,7 @@ jobs:
     - run: |
         sudo locale-gen en_US.UTF-8
         sudo update-locale
-    - uses: awalsh128/cache-apt-pkgs-action@master
+    - uses: awalsh128/cache-apt-pkgs-action@v1.6.1
       with:
         packages: lilypond timidity imagemagick fonts-noto-cjk graphviz plantuml ffmpeg
     - run: | # See also https://github.com/nguyenvulong/QA/issues/82