fix: use ternary for foreach single-item unwrap

[DragonBot00]

Problem

Step._get_foreach_items uses the Python and/or idiom to unwrap a single-item list:

return len(foreach_items) == 1 and foreach_items[0] or zip(*foreach_items)

When foreach_items[0] is a falsy value like 0, False, "", [], or {}, the and short-circuits to that falsy value, then or falls through to zip(*foreach_items). This causes a TypeError because scalars are not iterable.

Fix

Replace with a proper ternary expression:

return foreach_items[0] if len(foreach_items) == 1 else zip(*foreach_items)

This branches solely on the count of foreach items, not on the truthiness of the resolved value.

Fixes #6721