Update Xcode version in the build script

Author: Ali

buildbox/build-telegram.sh

@@ -5,7 +5,7 @@ set -e
 BUILD_TELEGRAM_VERSION="1"
 
 MACOS_VERSION="10.15"
-XCODE_VERSION="12.3"
+XCODE_VERSION="12.4"
 GUEST_SHELL="bash"
 
 VM_BASE_NAME="macos$(echo $MACOS_VERSION | sed -e 's/\.'/_/g)_Xcode$(echo $XCODE_VERSION | sed -e 's/\.'/_/g)"