CI: macos-13 is retired, drop it

Author: olleolleolle

.github/workflows/test.yml

@@ -21,9 +21,6 @@ jobs:
         exclude:
         - { os: macos-latest, ruby: '2.4' }
         - { os: macos-latest, ruby: '2.5' }
-        include:
-        - { os: macos-13, ruby: '2.4' }
-        - { os: macos-13, ruby: '2.5' }
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v6