🔧 Add Sphinx 9 jobs to CI matrix

Cover Sphinx 9 with the lowest compatible sphinx-needs (7) and the
highest (8). sphinx-needs <7 is incompatible with Sphinx 9.

Author: ubmarco

.github/workflows/ci.yml

@@ -57,6 +57,14 @@ jobs:
           - os: ubuntu-latest
             python: "3.14"
             tox-env: py314-sphinx8-needs8
+          # Sphinx 9 with lowest compatible sphinx-needs
+          - os: ubuntu-latest
+            python: "3.12"
+            tox-env: py312-sphinx9-needs7
+          # Sphinx 9 with highest sphinx-needs
+          - os: ubuntu-latest
+            python: "3.14"
+            tox-env: py314-sphinx9-needs8
           # minimal version on Windows
           - os: windows-latest
             python: "3.14"