Add linter step in CI

Author: erik-whiting

.github/workflows/obo-test.yml

@@ -20,6 +20,9 @@ jobs:
       - name: Install requirements
         run: |
           python3 -m pip install -r requirements.txt
+      - name: Run linter
+        run: |
+          tox -e lint
       - name: Run tests
         run: |
           make test