CI build-macos version from macOS 14 to macOS 15 (#2000)

macOS 15 has been officially released for some time, our current
`build-macos` workflow is still running on macOS 14.
This PR upgrades the macOS version used in our CI to macOS 15 to keep up
with the latest OS version and ensure long-term compatibility.

The `build-macos` CI workflow has successfully run on macOS 15:
https://github.com/vitahlin/valkey/actions/runs/14640672882

---------

Signed-off-by: vitah <vitahlin@gmail.com>
Signed-off-by: Vitah Lin <vitahlin@gmail.com>
Co-authored-by: Wen Hui <wen.hui.ware@gmail.com>

Author: vitahlin

.github/workflows/daily.yml

@@ -1130,7 +1130,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-13, macos-14]
+        os: [macos-13, macos-14, macos-15]
     runs-on: ${{ matrix.os }}
     if: |
       (github.event_name == 'workflow_dispatch' ||