remove macos-13 from CI

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

Author: alexrp

.github/workflows/build.yml

@@ -21,7 +21,6 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-13
           - macos-14
           - macos-15
           - macos-26