Fix __getattr__ in helpers.py throwing AttributeError for dotted module paths

[KushagraB424]

Description

This PR fixes a bug in airflow.utils.helpers.__getattr__ where the dynamic loading of deprecated functions (like render_template_as_native) was failing for dotted module paths (e.g. airflow.sdk.definitions.context).

When passing a dotted path to __import__ without the fromlist argument, it incorrectly returned the root package airflow instead of the target leaf module. This caused an AttributeError when the code subsequently tried to getattr the deprecated function directly on the root airflow module.

The fix replaces __import__(modpath) with importlib.import_module(modpath), which correctly returns the leaf module, allowing the compatibility shim and DeprecationWarning to function as intended.

• closes: Bug: __getattr__ in airflow.utils.helpers raises AttributeError for deprecated dotted imports #71198

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