GNUInstallDirs: Prefer system lib64 over conda lib when ambiguous

Update logic added by commit ecaca8c129 (GNUInstallDirs now aware of
conda lib directory requirements, 2021-09-08, v3.22.0-rc1~142^2).
When it is ambiguous if we are doing a conda install or a system
install prefer using the system library directory.

Fixes: #22962

Modules/GNUInstallDirs.cmake

@@ -253,7 +253,9 @@ if(NOT DEFINED CMAKE_INSTALL_LIBDIR OR (_libdir_set
     elseif(DEFINED ENV{CONDA_PREFIX})
       set(conda_prefix "$ENV{CONDA_PREFIX}")
       cmake_path(ABSOLUTE_PATH conda_prefix NORMALIZE)
-      if("${CMAKE_INSTALL_PREFIX}" STREQUAL conda_prefix)
+      if("${CMAKE_INSTALL_PREFIX}" STREQUAL conda_prefix AND
+         NOT ("${CMAKE_INSTALL_PREFIX}" MATCHES "^/usr/?$" OR
+              "${CMAKE_INSTALL_PREFIX}" MATCHES "^/usr/local/?$"))
         set(__system_type_for_install "conda")
       endif()
     endif()