downgrading macos to 13

Author: jmh530

.github/workflows/ci.yml

@@ -68,7 +68,7 @@ jobs:
 
   macos:
     name: '[macos] x86_64/${{ matrix.dc }}'
-    runs-on: macos-15-intel
+    runs-on: macos-13
     timeout-minutes: 60
     needs: setup
     # Only run if the setup phase explicitly defined compilers to be used