[Android][Gardener] Fixing ChromeTabbedActivityTest

ChromeTabbedActivityTest#testBackShouldCloseTab_Collaboration was
failing because of a NullPointerException.

When tabCreator creates a new tab Chrome tries to show an IPH message
related to version updates. The VersionUpdateIphHandler is responsible
for this and needs to get the VersioningMessageController from the
TabGroupSyncService.

Mock TabGroupSyncService is used in the test, but it doesn't specify
what should happen when getVersioningMessageController() is called. By
default, Mockito returns null. This null controller is then passed
along, leading to the NullPointerException when one of its methods is
invoked.

Mocking the VersioningMessageController should fix the test.

Change-Id: If0a752e1a4cc5353d3fd5e3c32975be4ef1dee27
Bug: 436750862
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6827381
Owners-Override: Ivana Žužić <izuzic@google.com>
Reviewed-by: Adem Derinel <derinel@google.com>
Commit-Queue: Ivana Žužić <izuzic@google.com>
Auto-Submit: Ivana Žužić <izuzic@google.com>
Cr-Commit-Position: refs/heads/main@{#1498107}