tests: Run black in CI.

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
           sudo apt-get install -y firefox
         fi
         python -m pip install --upgrade pip
-        pip install flake8 codespell pytest selenium
+        pip install -e .[dev]
         pip install -r requirements.txt --require-hashes
     - name: Install
       run: |
@@ -52,6 +52,9 @@ jobs:
     - name: Run codespell
       run: |
         codespell --check-filenames --disable-colors --quiet-level=7 --ignore-words=tests/lint/spelling.ignore-words.txt -S .git,.eggs,.tox,pgp,*.pyc,*basicswap/contrib,*basicswap/interface/contrib,*mnemonics.py,bin/install_certifi.py,*basicswap/static
+    - name: Run black
+      run: |
+        black --check --diff --exclude="contrib" .
     - name: Run test_other
       run: |
         pytest tests/basicswap/test_other.py