Fix lint workflow: pin click<8.1.0 for black==20.8b1 compatibility

black==20.8b1 imports click._unicodefun which was removed in click 8.1.0.
Pin click to a compatible version before installing [test] extras.

Author: yanjunqiAz

.github/workflows/check-formatting.yml

@@ -20,6 +20,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip setuptools wheel
         python setup.py install_egg_info
+        pip install "click<8.1.0"
         pip install -e .[test]
     - name: Check code format with black and isort
       run: |