FindPython: Do not cache computed result variables

Since commit 06d9e67fbd (FindPython: Add capability to specify directly
artifacts, 2019-08-15, v3.16.0-rc1~157^2) we accidentally add the result
variables `Python*_LIBRARY_RELEASE` and `Python*_LIBRARY_DEBUG` to the
cache.  They are always computed from other results and so should not be
presented to users in cmake-gui and ccmake to edit.

Issue: #20362

Modules/FindPython/Support.cmake

@@ -2078,7 +2078,7 @@ if ("Development" IN_LIST ${_PYTHON_PREFIX}_FIND_COMPONENTS
   # finalize library version information
   _python_get_version (LIBRARY PREFIX _${_PYTHON_PREFIX}_)
 
-  set (${_PYTHON_PREFIX}_LIBRARY_RELEASE "${_${_PYTHON_PREFIX}_LIBRARY_RELEASE}" CACHE FILEPATH "Path to a library." FORCE)
+  set (${_PYTHON_PREFIX}_LIBRARY_RELEASE "${_${_PYTHON_PREFIX}_LIBRARY_RELEASE}")
 
   if (_${_PYTHON_PREFIX}_LIBRARY_RELEASE AND NOT EXISTS "${_${_PYTHON_PREFIX}_LIBRARY_RELEASE}")
     set (_${_PYTHON_PREFIX}_Development_REASON_FAILURE "Cannot find the library \"${_${_PYTHON_PREFIX}_LIBRARY_RELEASE}\"")
@@ -2237,7 +2237,7 @@ if ("Development" IN_LIST ${_PYTHON_PREFIX}_FIND_COMPONENTS
   endif()
 
   # define public variables
-  set (${_PYTHON_PREFIX}_LIBRARY_DEBUG "${_${_PYTHON_PREFIX}_LIBRARY_DEBUG}" CACHE FILEPATH "Path to a library." FORCE)
+  set (${_PYTHON_PREFIX}_LIBRARY_DEBUG "${_${_PYTHON_PREFIX}_LIBRARY_DEBUG}")
   _python_select_library_configurations (${_PYTHON_PREFIX})
 
   set (${_PYTHON_PREFIX}_RUNTIME_LIBRARY_RELEASE "${_${_PYTHON_PREFIX}_RUNTIME_LIBRARY_RELEASE}")