CI: Update runner from macos-13 to macos-15-intel

Author: amotl

.github/workflows/release-app.yml

@@ -24,7 +24,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [
-          "macos-13",        # Intel
+          "macos-15-intel",  # Intel
           "macos-latest",    # ARM
           "ubuntu-latest",   # Intel
           "windows-latest",  # Intel