[BUG] Fix ValueError in _check_list_of_dict_table when encountering non-dict elements

[Kayd-06]

Reference Issues/PR

Fixes an undiscovered bug in _check_list_of_dict_table validation.

What does this implement/fix? Explain your changes.

Fixes a bug in skpro.datatypes._table._check._check_list_of_dict_table where a generator expression was incorrectly passed to np.where().

When invalid elements (non-dictionaries) were verified by this function, it attempted to return an error message containing their indices. By passing not isinstance(x, dict) for x in obj directly into np.where(), it inadvertently caused a ValueError: Calling nonzero on 0d arrays is not allowed. instead of returning the validation constraint violation.

This commit replaces the faulty np.where() generator with a standard list comprehension [i for i, x in enumerate(obj) if not isinstance(x, dict)]. This correctly formats the invalid indices into the error string and prevents the validation function itself from crashing.

Does your contribution introduce a new dependency? If yes, which one?

No.

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