fix(ci): use macos-15-intel for x86_64 testing

Author: sverrejoh

.github/workflows/CI.yml

@@ -103,7 +103,7 @@ jobs:
       fail-fast: false
       matrix:
         settings:
-          - host: macos-13
+          - host: macos-15-intel
             target: x86_64-apple-darwin
           - host: macos-latest
             target: aarch64-apple-darwin