Provide block label in failure output

It would be great to see the block label belonging to the failing assertion. Below added the new line beginning with the word Context:

Context: 'there are still three elements'
Condition not satisfied:

numbers.size() == 2
|       |      |
|       3      false
[1, 2, 3]

Expected :2

Actual   :3

With that it would be easier to understand the context of the failure message without looking at the code.

Sample feature for the failure above:

def "test set modification"() {
    given: 'a set with three element'
    Set numbers = [1, 2, 3]

    when: 'adding an existing element'
    numbers.add(2)

    then: 'there are still three elements'
    numbers.size() == 2
}

Start by locating the failure output generated for the sample Groovy feature and its failing assertion. Reproduce the shown output, then verify that the assertion's block label appears as Context while the existing condition, expected, and actual sections remain intact.