ci: update macos runner images

Add macos-15 runners. Remove the deprecated macos-13 runners.

Fixes: https://github.com/libuv/libuv/issues/4965

.github/workflows/CI-unix.yml

@@ -80,7 +80,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-13, macos-14]
+        os: [macos-14, macos-15]
     steps:
       - uses: actions/checkout@v6
       - name: Envinfo
@@ -122,7 +122,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-13, macos-14]
+        os: [macos-14, macos-15]
     steps:
       - uses: actions/checkout@v6
       - name: Configure

.github/workflows/sanitizer.yml

@@ -55,7 +55,7 @@ jobs:
           fi
 
   sanitizers-macos:
-    runs-on: macos-13
+    runs-on: macos-14
     strategy:
       matrix:
         config: