ci: use macOS 15 Sequoia

Author: nto

.github/workflows/test-suite.yaml

@@ -57,8 +57,8 @@ jobs:
             os: macos-13
             compiler: xcode
 
-          - name: macos-14-arm64-xcode
-            os: macos-14
+          - name: macos-15-arm64-xcode
+            os: macos-15
             compiler: xcode
             luajit: false