CI: do not test Sphinx 7.3

Author: tacaswell

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
         os: [Ubuntu]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
         sphinx-version:
-          ["sphinx==6.0", "sphinx==6.2", "sphinx==7.0", "sphinx>=7.2"]
+          ["sphinx==6.0", "sphinx==6.2", "sphinx==7.0", "sphinx>=7.2,<7.3"]
     steps:
       - uses: actions/checkout@v4