add macos-{15,26}-intel to CI

Author: alexrp

.github/workflows/build.yml

@@ -23,7 +23,9 @@ jobs:
         os:
           - macos-14
           - macos-15
+          - macos-15-intel
           - macos-26
+          - macos-26-intel
           - ubuntu-22.04
           - ubuntu-22.04-arm
           - ubuntu-24.04