Add intltool

Fixes installation of python-apt:

      running build_i18n
      intltool-update -p -g python-apt
      error: command 'intltool-update' failed: No such file or directory
      [end of output]

Author: freyes

.github/workflows/tox.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Install dependencies
       run: |
         sudo apt-get update
-        sudo apt-get install libapt-pkg-dev
+        sudo apt-get install libapt-pkg-dev intltool
         python -m pip install --upgrade pip
         python -m pip install tox tox-gh-actions
     - name: Test with python ${{ matrix.python-version }}