Bump minimum Python version to 3.8 (#1876)

* Bump minimum Python version to 3.8

* typing_extensions.Literal -> typing.Literal

* ns-dev-test

* typing_extensions.get_args => typing.get_args

* Format with older version of black

* Bump `black`

* Run black

.github/workflows/core_code_checks.yml

@@ -15,10 +15,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - name: Set up Python 3.7.13
+      - name: Set up Python 3.8.13
         uses: actions/setup-python@v4
         with:
-          python-version: '3.7.13'
+          python-version: '3.8.13'
       - uses: actions/cache@v2
         with:
           path: ${{ env.pythonLocation }}