macos.yml: macOS 13 hosted runner image is closing down

https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

Author: k0kubun

.github/workflows/macos.yml

@@ -45,8 +45,6 @@ jobs:
             os: macos-14
           - test_task: check
             os: macos-15
-          - test_task: check
-            os: macos-13
       fail-fast: false
 
     env: