Fix test dir

Author: hukkin

.github/workflows/tests.yml

@@ -45,7 +45,7 @@ jobs:
         pip install .[testing,linkify]
     - name: Run pytest
       run: |
-        pytest --cov=markdown_it --cov-report=xml --cov-report=term-missing
+        pytest tests/ --cov=markdown_it --cov-report=xml --cov-report=term-missing
     - name: Upload to Codecov
       if: matrix.python-version == '3.7' && github.repository == 'executablebooks/markdown-it-py'
       uses: codecov/codecov-action@v1