CI: OS doesn't need to be in test matrix

Author: amotl

.github/workflows/main.yml

@@ -18,16 +18,14 @@ jobs:
 
   tests:
 
-    runs-on: ${{ matrix.os }}
+    runs-on: "ubuntu-latest"
     strategy:
       fail-fast: false
       matrix:
-        os: ["ubuntu-latest"]
         python-version: ["3.10", "3.14"]
         sphinx-version: ["6.*", "7.*"]
         include:
-          - os: "ubuntu-latest"
-            python-version: "3.9"
+          - python-version: "3.9"
             sphinx-version: "7.*"
 
     env:
@@ -37,7 +35,6 @@ jobs:
     name: "
     Sphinx ${{ matrix.sphinx-version }}
     Python ${{ matrix.python-version }}
-    OS ${{ matrix.os }}
     "
     steps: