Update macOS version in unit test workflow (#441)

Author: rob93c

.github/workflows/unit-test.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, windows-latest, macos-13 ] # pin macos to latest x64 image
+        os: [ ubuntu-latest, windows-latest, macos-15-intel ] # pin macos to latest x64 image
     steps:
       - name: Checkout code changes
         uses: actions/checkout@v6