Fix cleanup ops for inferred schema

[NathalieCharbel]

Description

Fixes AttributeError that occurs during schema cleanup in SchemaFromTextExtractor when LLMs return node/relationship types as strings instead of the expected dictionary format.

Changes:

• Added defensive type checking in _filter_nodes_without_labels and _filter_relationships_without_labels methods
• Updated unit tests

Type of Change

• New feature
• Bug fix
• Breaking change
• Documentation update
• Project configuration change

Complexity

Complexity: low

How Has This Been Tested?

• Unit tests
• E2E tests
• Manual tests

Checklist

The following requirements should have been met (depending on the changes in the branch):

• Documentation has been updated
• Unit tests have been updated
• E2E tests have been updated
• Examples have been updated
• New files have copyright header
• CLA (https://neo4j.com/developer/cla/) has been signed
• CHANGELOG.md updated if appropriate

[stellasia]

I was a bit afraid that we will fix things without knowing what is broken exactly. But in practice, we don't know what the LLM will choose as a label even if the JSON structure is correct, so I convinced myself that this fix is good enough, or at least consistent with the rest of the component :)

Thanks Nathalie!