Update HTMLTidy.yml

Author: guwirth

.github/workflows/HTMLTidy.yml

@@ -19,6 +19,10 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: '3.x'
+    - name: Install xmllint
+      run: |
+         sudo apt-get update
+         sudo apt-get install libxml2-utils
     - name: Install HTML Tidy
       run: |
          wget https://github.com/htacg/tidy-html5/releases/download/5.8.0/tidy-5.8.0-Linux-64bit.deb