[headless] De-flake HeadlessMode*CreateTargetSecondaryScreen test

Before logging the current screen label after creating a new target, the
test now checks if the target is on the expected screen and if not,
waits for the 'currentscreenchange' event.

Bug: 446689489
Change-Id: I4733ee81a345aad69a745e6654a42764ba4f4fa8
Cq-Include-Trybots: luci.chromium.try:mac13-tests,mac14-tests
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8207961
Auto-Submit: Peter Kvitek <kvitekp@chromium.org>
Commit-Queue: Peter Kvitek <kvitekp@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1674948}