update to macos 15

Author: aashishpatil-g

.github/workflows/spm.yml

@@ -53,7 +53,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [macos-14]
+        os: [macos-15]
         # GitHub actions' runners do not include visionOS. https://github.com/actions/runner-images/issues/10559
         target: [iOS, macOS, catalyst]
         xcode: [Xcode_16.2]