Update x64 build to Mac 15 (13 deprecated, 14 x64 is large-only)

Author: pimterry

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
             os: "windows-2022"
           - platform: mac
             arch: x64
-            os: "macos-13"
+            os: "macos-15-intel"
           - platform: mac
             arch: arm64
             os: "macos-14"