Add texgyre build dependency to GH Action

Author: erelson

.github/workflows/push_docs_to_github.io.yml

@@ -30,6 +30,7 @@ jobs:
               latexmk \
               texlive-latex-recommended \
               texlive-latex-extra \
+              texgyre \
               fonts-texgyre \
               fonts-texgyre-math
           # `python3-sphinx` pulls in docutils, jinja2, pygments, babel, etc.