Update Xcode selection

Author: jmroot

.github/workflows/main.yml

@@ -41,7 +41,7 @@ jobs:
           case "`uname -r`" in
             22.*) sudo xcode-select --switch /Applications/Xcode_14.3.1.app/Contents/Developer
                 ;;
-            23.*) sudo xcode-select --switch /Applications/Xcode_16.app/Contents/Developer
+            23.*) sudo xcode-select --switch /Applications/Xcode_15.4.app/Contents/Developer
                 ;;
           esac
       - name: Configure MacPorts Base