Use macos-15 runner in build workflow

Bump GitHub Actions runner from macos-14 to macos-15 in the build-python workflow so CI uses the updated macOS image for building Python for iOS and macOS.

Author: FeodorFitsner

.github/workflows/build-python.yml

@@ -13,7 +13,7 @@ env:
 jobs:
   build-darwin:
     name: Build Python for iOS and macOS
-    runs-on: macos-14
+    runs-on: macos-15
     permissions:
       contents: write