fix(text): don't crash on --query lists mixing scalars and objects

[devteamaegis]

What's broken

--output text exits 255 on a --query multi-select list that mixes a scalar with an object. --output json handles the same data fine.

$ aws ec2 describe-instances --output text \
    --query '[Reservations[0].Instances[0].InstanceId, Reservations[0].Instances[0].State]'
AttributeError: 'str' object has no attribute 'items'

[InstanceId, State] is ordinary JMESPath — InstanceId is a string and State is an object — so any query of that shape kills the command. Nothing is printed at all.

Why it happens

_format_list decides a list is "a list of dicts" if any element is a dict:

if any(isinstance(el, dict) for el in item):
    all_keys = _all_scalar_keys(item)

but _all_scalar_keys then calls .items() on every element, so one non-dict in the list raises. The sibling branch for nested lists already tolerates mixed content (_partition_list); this branch did not.

The fix

Skip non-dict elements when collecting scalar keys. The loop right below already routes each element through _format_text, which renders scalars and nested lists on their own — so the mixed list now prints:

i-123
16	running

The test

test_dicts_mixed_with_scalars and test_dicts_mixed_with_lists in tests/unit/test_text.py. Both fail on develop with the AttributeError and pass with the fix:

$ python -m pytest tests/unit/test_text.py -k dicts_mixed     # before
E   AttributeError: 'str' object has no attribute 'items'
2 failed, 25 deselected

$ python -m pytest tests/unit/test_text.py                    # after
27 passed

tests/unit/test_text.py tests/unit/output/ tests/unit/test_table.py — 59 passed.