python bindings: get version from package.xml (#556)

Requires gz-cmake4 4.1.0.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

python/CMakeLists.txt

@@ -1,8 +1,9 @@
 # Detect if we are doing a standalone build of the bindings, using an external gz-transport
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   cmake_minimum_required(VERSION 3.22.1)
-  set(GZ_TRANSPORT_VER 14)
-  project(gz-transport${GZ_TRANSPORT_VER}-python VERSION ${GZ_TRANSPORT_VER})
+  find_package(gz-cmake4 4.1.0 REQUIRED)
+  gz_get_package_xml_version(${CMAKE_SOURCE_DIR}/../package.xml PACKAGE_XML)
+  project(gz-transport${PACKAGE_XML_VERSION_MAJOR}-python VERSION ${PACKAGE_XML_VERSION})
   find_package(gz-transport${PROJECT_VERSION_MAJOR} REQUIRED)
   set(PROJECT_LIBRARY_TARGET_NAME "gz-transport${PROJECT_VERSION_MAJOR}::gz-transport${PROJECT_VERSION_MAJOR}")
   # require python dependencies to be found