Cygwin: Avoid legacy warnings in RunCMake.DisallowedCommands test

Set the minimum required version of CMake high enough to avoid the
warning for CMAKE_LEGACY_CYGWIN_WIN32.  The warning appears on stderr
and breaks the expected output matching.
Merge topic 'remove-old-commands-by-policy' into next

4ea27bc Cygwin: Avoid legacy warnings in RunCMake.DisallowedCommands test