Switch to macos-15-intel runner (#2650)

https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

Author: ntkme

.github/workflows/build-macos.yml

@@ -19,7 +19,7 @@ jobs:
       matrix:
         include:
           - arch: x64
-            runner: macos-13
+            runner: macos-15-intel
           - arch: arm64
             runner: macos-latest