Fix WindowMagnificationControllerTest flaky

The bounds change callback rely on onLayoutChangeListener
The failure reason is that the calbkack is invoked twice
but couldn't repro it locally.
To fix it we simplfy the verification to avoid
TooManyActualInvocations

Bug: 188889181
Test: run the failed test 100 times
Change-Id: Ib44fb399cc091ac9711e19ec761d6cf5eaaea40f