Rework test matrix

Author: lafrech

.github/workflows/python-app.yml

@@ -14,14 +14,18 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9"]
+        python-version: ["3.8", "3.9"]
         sphinx-version: [
           "6.0.*",
           "5.0.*",
           "4.5", "4.4", "4.3", "4.2", "4.1", "4.0.*",
           "3.5.*", "3.4.*", "3.2.*",  "3.1.*", "3.0.*",
         ]
         include:
+          - python-version: "3.7"
+            sphinx-version: ""
+          - python-version: "3.7"
+            sphinx-version: "3.5"
           - python-version: "3.10"
             sphinx-version: ""
           - python-version: "3.10"