Install dmtx-utils for testing in GH action.

.github/workflows/python-package.yml

@@ -26,6 +26,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
+        apt-get update && apt-get install -y dmtx-utils
         python -m pip install --upgrade pip
         python -m pip install pytest
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi