Update rapids_find_generate_module to cmake 3.23 (#256)

Missed as part of #227 was an update to the policy version set in `rapids_find_generate_module`

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - Bradley Dice (https://github.com/bdice)

URL: #256

rapids-cmake/find/generate_module.cmake

@@ -16,7 +16,7 @@
 include_guard(GLOBAL)
 
 cmake_policy(PUSH)
-cmake_policy(VERSION 3.20)
+cmake_policy(VERSION 3.23)
 
 #[=======================================================================[.rst:
 rapids_find_generate_module