sensors: Always restore focus in virtual-sensor-updates.https.window.js

Follow-up to https://crrev.com/c/5272509: this test switches focus to
the iframe but does not explicitly focus the main window again, which
causes issues for any tests that come after it.

Change-Id: I359a2229ce1dc421ad5c6119ab5512e846fe7382
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5317429


Commit-Queue: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Auto-Submit: Raphael Kubo Da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/main@{#1264065}