Cygwin: Avoid legacy warnings in RunCMake.CMP004[1235] tests

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 'cygwin-RunCMake-tests' into next

5e4b8871 Cygwin: Avoid legacy warnings in RunCMake.CMP004[1235] tests