kconfig: tests: test if new symbols in choice are asked

If new choice values are added with new dependency, and they become
visible during user configuration, oldconfig should recognize them
as (NEW), and ask the user for choice.

This issue was fixed by commit 5d09598d ("kconfig: fix new choices
being skipped upon config update").

This is a subtle corner case.  Add a test case to avoid breakage.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>