[CI] Upgrade to macos-15

Author: straight-shoota

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04, macos-13, macos-14]
+        os: [ubuntu-24.04, macos-15-intel, macos-15]
         crystal: [latest, nightly]
         include:
           - os: windows-2022