Help: Verification target also sets CXX_SCAN_FOR_MODULES to false

4fd596c34c (cmGeneratorTarget: disable C++ module scanning for
verify targets, 2023-12-11) added the CXX_SCAN_FOR_MODULES
property to the list of properties set to false in the verification target
when VERIFY_INTERFACE_HEADER_SETS is true, but it didn't update
the documentation of that target property. This adds the missing
doc update.