GitHub Actions: Update macOS runner to version 13

This version comes with 4 CPUs instead of 3.

Change-Id: I0a5de644e668a77a9cbda9fa57b6a322351dafa4
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

.github/workflows/build_cmake.yml

@@ -49,7 +49,8 @@ jobs:
           }
         - {
             name: "macOS Latest Clang", artifact: "macos-universal",
-            os: macos-latest,
+            # TODO: move back to macos-latest when macos-latest is 13 or higher
+            os: macos-13,
             cc: "clang", cxx: "clang++"
           }