ci: use macos-15-intel for x86 tests

The macOS-13 based runner images are being deprecated, switching to
macOS-15 (macos-15-intel) and macOS 15 arm64 (macos-latest) instead. For
more details see actions/runner-images#13046

Author: santhoshtr

.github/workflows/python.yaml

@@ -95,9 +95,9 @@ jobs:
     strategy:
       matrix:
         platform:
-          - runner: macos-13
+          - runner: macos-15-intel
             target: x86_64
-          - runner: macos-14
+          - runner: macos-latest
             target: aarch64
     steps:
       - uses: actions/checkout@v4