tests: test PHP >= 8 on macOS 15

Author: firstred

.github/workflows/test.yaml

@@ -5,7 +5,7 @@ jobs:
         runs-on: ${{ matrix.operating-system }}
         strategy:
             matrix:
-                operating-system: [ 'ubuntu-24.04', 'windows-2025', 'macos-latest' ]
+                operating-system: [ 'ubuntu-24.04', 'windows-2025', 'macos-15' ]
                 php-versions: [ '8.0', '8.1', '8.2', '8.3', '8.4', '8.5' ]
                 include:
                     - operating-system: 'ubuntu-24.04'