use macos-15-intel for x86_64 builds

Author: mattip

.github/workflows/wheel.yml

@@ -29,8 +29,8 @@ jobs:
           - { os: ubuntu-latest, PLAT: x86_64, INTERFACE64: '0', MB_ML_VER: '2014', MB_ML_LIBC: manylinux}
           - { os: ubuntu-latest, PLAT: x86_64, INTERFACE64: '1', MB_ML_VER: '2014', MB_ML_LIBC: manylinux}
 
-          - { os: macos-latest, PLAT: x86_64, INTERFACE64: '0', MB_ML_LIBC: macosx}
-          - { os: macos-latest, PLAT: x86_64, INTERFACE64: '1', MB_ML_LIBC: macosx}
+          - { os: macos-15-intel, PLAT: x86_64, INTERFACE64: '0', MB_ML_LIBC: macosx}
+          - { os: macos-15-intel, PLAT: x86_64, INTERFACE64: '1', MB_ML_LIBC: macosx}
 
           - { os: macos-latest, PLAT: arm64, INTERFACE64: '0', MB_ML_LIBC: macosx}
           - { os: macos-latest, PLAT: arm64, INTERFACE64: '1', MB_ML_LIBC: macosx}