Remove deprecated macos-13 from CI

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

Author: meator

.github/workflows/build.yml

@@ -168,7 +168,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-13, macos-14, macos-15]
+        os: [macos-14, macos-15]
     runs-on: ${{ matrix.os }}
     needs: [upload-src]
     steps: