removing macos-13: deprecated

Author: WolfgangWaltenberger

.github/workflows/validation.yml

@@ -22,7 +22,7 @@ jobs:
 #        python-version: [ "3.13" ]
 #        os: [ubuntu-latest ]
         python-version: [ "3.9", "3.10", "3.11", "3.12", "3.13" ]
-        os: [ubuntu-22.04, ubuntu-24.04, macos-13, macos-14, macos-15 ]
+        os: [ubuntu-22.04, ubuntu-24.04, macos-14, macos-15 ]
 
     steps:
     - uses: actions/checkout@v5