text: Title: Change default `FOR IN ZIP` mode from `SHORTEST` to `STRICT`
  Body: RF 6.1 made it possible to configure what to do if lengths of lists iterated using `FOR IN ZIP` are different (#4682). The old default behavior to silently ignore items in longer lists (i.e. `SHORTEST` mode) was preserved, but the plan is to deprecate it in RF 7.0 (#4685). In RF 8 we can then change the default so that lengths must match (i.e. `STRICT` mode). The main motivation is avoiding false positives. See #4682 for mode details.