CCE happens because we always select expandable node on click and
because the JUnit related selection listener code queries the selection
from the widget instead of using selection from selection event while
reacting on selection change. This is unusual, but allowed.

However, setting selection in first place is actually not needed, the
only reason to do so was to reveal last element after expanding, so that
user can simply click few times if needed. Revealing shown items however
can be done without selection, so we don't run in such corner cases
here.

Fixes https://github.com/eclipse-platform/eclipse.platform.ui/issues/1360