fix(step): safely unwrap single foreach item when resolving to falsy scalar (#6721)

[MyDude92]

Closes #6721

📑 Description

Step._get_foreach_items previously used the Python ternary anti-pattern return len(foreach_items) == 1 and foreach_items[0] or zip(*foreach_items). When a single foreach reference legitimately evaluates to 0 or False, the expression falls through to zip(*foreach_items) which raises TypeError: Value after * must be an iterable, not int / bool.

Changes Made

1. keep/step/step.py: Replaced anti-pattern with standard conditional expression: return foreach_items[0] if len(foreach_items) == 1 else zip(*foreach_items).
2. tests/test_steps.py: Added unit test test_get_foreach_items_falsy_scalar validating single foreach evaluation when resolved context yields 0 or False.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed