patch 9.2.0430: tests: Test_shortmess_F3() is flaky on MS-Windows

patch 9.2.0430: tests: Test_shortmess_F3() is flaky on MS-Windows

Problem:  tests: Test_shortmess_F3() is flaky on MS-Windows
Solution: Increase the sleep to 3s (Yasuhiro Matsumoto)

On MS-Windows time_differs() treats mtime as unchanged unless st_mtime
differs by more than 1 second, so a 2-second sleep can fall short when
the two writes straddle a second boundary. Bump the non-nanotime sleep
to 3 seconds.

closes: #20117

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>