patch 9.1.1990: tests: Test_term_gettty() fails when using conpty on Windows

patch 9.1.1990: tests: Test_term_gettty() fails when using conpty on Windows

Problem:  tests: Test_term_gettty() fails when using conpty on Windows,
          CI uses winpty, so this test passes.
Solution: Skip the test Test_term_gettty(). Since conpty communicates
          via anonymous pipes, there is no name that can be obtained
          with term_gettty() (Muraoka Taro)

closes: #18954

Signed-off-by: Muraoka Taro <koron.kaoriya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>