Remove macos-12 from CI.

https://github.blog/changelog/2024-08-19-notice-of-upcoming-deprecations-and-breaking-changes-in-github-actions-runners/

Author: alexrp

.github/workflows/build.yml

@@ -21,7 +21,6 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-12
           - macos-13
           - macos-14
           - ubuntu-20.04