Build/Test Tools: Update MacOS GitHub Actions runner.

The `macos-13` runner image is deprecated with support set to be fully removed next month. This updates the build process testing workflow’s MacOS job to use the `macos-15-intel` runner in the 6.3 branch.

The `-intel` part is required because older branches of WordPress use Node.js `14.x` which never supported `arm64` environments. The `macos-15-intel` image will be the last `x86_64` runner published for GitHub Actions and will be supported until August 2027.

See #64246.

git-svn-id: https://develop.svn.wordpress.org/branches/6.3@61226 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

.github/workflows/test-build-processes.yml

@@ -81,7 +81,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ macos-13 ]
+        os: ['macos-15-intel']
         directory: [ 'src', 'build' ]
     with:
       os: ${{ matrix.os }}