fix: reject scalar context foreach sources

tests/core/test_schema_navigation.py

@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+from wf_core.schema_navigation import SchemaNavigator
+
+
+def test_array_type_does_not_require_an_items_schema() -> None:
+    """Unconstrained array elements do not make the collection non-array."""
+    view = SchemaNavigator({"type": "array"}).root
+
+    assert view.is_array()