Override phpunit assertTag method to stop errors

This method throws a deperecation error in phpunit
that we dont want to see (and dont want to break
travis tests).

Nothing this method uses is beign deprecated thus
we can override the method and not need to worry
about the error or it vanishing in the future!

Bug: 69505
Change-Id: I0eb63be390b4fdf416635dd8e8a2ad94615e6a47