Revert "Try running on all macos-latest / Python version combinations"

This reverts commit e4e5c69.

Author: matt-graham

.github/workflows/tests.yml

@@ -28,7 +28,10 @@ jobs:
     strategy:
       matrix:
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-latest]
+        include:
+          - os: macos-latest
+            python-version: "3.8"
       fail-fast: false
 
     steps: