CI: __sudo__ apt-get... for install.

.github/workflows/test_linux.yml

@@ -31,7 +31,7 @@ jobs:
         python -m pip install hatch
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
         # latexmk
-        apt-get -y install latexmk texlive-extra
+        sudo apt-get -y install latexmk texlive-extra
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names