user32/tests: Disable automatic shell restart during SetShellWindow tests.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=27438

Your paranoid android.


=== w864 (32 bit win) ===
win.c:2305: Test failed: expected !100
win.c:2305: Test failed: expected !100

=== w864 (64 bit win) ===
win.c:2305: Test failed: expected !100
win.c:2305: Test failed: expected !100