[suggestion] rename skip to when or precondition

[fokion]

In order to skip a test case or a step the assertions of the skip block MUST be false and that is confusing. As when we have all the assertions valid under the skip block then it will execute it. I propose to rename this block to when or precondition as those assertions are preconditions of executing the step or the case

[fokion]

https://github.com/ovh/venom/discussions/696

[yesnault]

see discussion #696