ci: switch to macos-15-intel for older python versions

Author: smacke

.github/workflows/ci.yml

@@ -13,11 +13,11 @@ jobs:
         python-version: [ '3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14' ]
         include:
           - python-version: '3.7'
-            os: 'macos-13'
+            os: 'macos-15-intel'
           - python-version: '3.8'
-            os: 'macos-13'
+            os: 'macos-15-intel'
           - python-version: '3.9'
-            os: 'macos-13'
+            os: 'macos-15-intel'
           - python-version: '3.10'
             os: 'macos-latest'
           - python-version: '3.11'