Add a new job to run unit tests

.github/workflows/main.yml

+# This workflow will run the unit tests and create a new image on the Docker Hub.
+# At least for now, the image will be created regardless of whether the tests are run successfully or not.
+#
+# References:
+#   - https://docs.github.com/en/actions/guides/building-and-testing-python
+#   - https://github.com/marketplace/actions/slack-notify
+
 name: Building Docker containers
 
 # Triggers the workflow on push or pull request events
 on: [push, pull_request]
 
 jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.8'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r rnacentral/requirements.txt
+          pip install -r rnacentral/requirements_dev.txt
+
+      - name: Run tests
+        run: |
+          python rnacentral/manage.py test sequence_search
+
   initial-notification:
     runs-on: ubuntu-latest
     steps: