ci: migrate from macos-13 to macos-15-intel

macos-13 runners are being deprecated by GitHub Actions.
See actions/runner-images#13046

Author: avrabe

.github/workflows/production-readiness.yml

@@ -117,7 +117,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-22.04, macos-13]
+        os: [ubuntu-22.04, macos-15-intel]
 
     steps:
       - uses: actions/checkout@v5