Include the encryption extra in the CI.

This is required for mypy to pass.

.github/workflows/pytest.yml

@@ -25,7 +25,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        pip install .[dev,tools]
+        pip install .[dev,tools,encryption]
     - name: Test with pytest
       run: |
         pytest -vvv --mypy