Add black_multi_python workflow.

.github/workflows/black_multi_python.yml

@@ -0,0 +1,27 @@
+name: multi-python black check on push and PR
+#
+# Run the black formatting in multiple Python versions
+#
+on: [push, pull_request]
+
+jobs:
+  black-check-multi-python:
+     runs-on: ubuntu-latest
+     strategy:
+       fail-fast: false
+       matrix:
+         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+     steps:
+     - uses: actions/checkout@v4
+     - name: Set up Python ${{ matrix.python-version }}
+       uses: actions/setup-python@v3
+       with:
+         python-version: ${{ matrix.python-version }}
+     - name: Install dependencies
+       run: |
+         python -m pip install --upgrade pip
+         pip install black
+     - name: Analysing the code with black
+       run: |
+         cd python
+         black --check --config python/pyproject.toml ../cime_config/SystemTests ../cime_config/buildlib ../cime_config/buildnml