CI: Update tests workflow to deprecate macOS 13 and add macOS 15

Author: PatTheMav

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
   test-bot:
     strategy:
       matrix:
-        os: [ubuntu-22.04, ubuntu-24.04, macos-13, macos-14]
+        os: [ubuntu-22.04, ubuntu-24.04, macos-14, macos-15]
     runs-on: ${{ matrix.os }}
     env:
       HOMEBREW_GITHUB_API_TOKEN: ${{ secrets.HOMEBREW_API_TOKEN }}