CI: move Intel macOS job to macos-15-intel runner

Author: crisdosaygo

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
       matrix:
         include:
           - os: macOS (Intel)
-            runner: macos-13
+            runner: macos-15-intel
           - os: macOS (ARM)
             runner: macos-14
           - os: ubuntu-22.04