.github/workflows/test: Fix syntax

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         sphinx_version: ["", "~=6.0.0", "~=5.0.0"]
         python_version: ["3.8", "3.10", '3.x']
-        #exclude:
+        exclude:
           - {sphinx_version: "~=6.0.0", python_version: '3.8'}
         #  - {sphinx_version: "~=4.0.0", python_version: '3.10'}
         #  - {sphinx_version: "~=3.0.0", python_version: '3.x'}