Sphinx 4 doesn't support Python >=3.10

Author: sciencewhiz

.github/workflows/workflow.yml

@@ -26,12 +26,16 @@ jobs:
     strategy:
       matrix:
         python-version: ['3.8', '3.9', '3.10', '3.11', '3.12', 'pypy3.10']
-        sphinx-version: ['4', '5', '6', '7']
+        sphinx-version: ['5', '6', '7']
         include:
           - python-version: '3.7'
             sphinx-version: '3'
           - python-version: '3.7'
             sphinx-version: '2'
+          - python-version: '3.8'
+            sphinx-version: '4'
+          - python-version: '3.9'
+            sphinx-version: '4'
     name: "Test Extension - Python(${{ matrix.python-version }}), Sphinx(${{ matrix.sphinx-version }})"
     steps:
       - uses: actions/checkout@v4