fix(external_task_sensor): fallback to execution_date key for execution_date_fn context (#52236)

[yeswanth-s1th]

Closes #52236.

What this PR does:

• In _handle_execution_date_fn, tries context['logical_date'], then the legacy context['execution_date'], then dag_run.run_after.
• Adds a pytest to validate the fallback to execution_date.

This prevents a KeyError for users whose context lacks logical_date but still have execution_date.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst)
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our pre-commits will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
• Always keep your Pull Requests rebased, otherwise your build might fail due to changes not related to your commits.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: dev@airflow.apache.org
  Slack: https://s.apache.org/airflow-slack

[gopidesupavan]

@yeswanth-bf added comment in issue, to get the log

[gopidesupavan]

LGTM

[gopidesupavan]

@yeswanth-bf tests are failing ..

[gopidesupavan]

compact tests failing, please take look at these test references: providers/standard/tests/unit/standard/operators/test_weekday.py

[gopidesupavan]

@yeswanth-s1th do you need any help give me a shout.

[gopidesupavan]

@yeswanth-s1th any update on the test fixes? happy to fork these changes and add you as co-author

[yeswanth-s1th]

@yeswanth-s1th any update on the test fixes? happy to fork these changes and add you as co-author

@gopidesupavan
To optimize attribution visibility, could we keep my original commits authored by me, and add you as Co-authored-by: on any new/amended ones? If you end up squashing, would you mind setting me as the commit Author and yourself as a co-author so the signal remains intact?

Co-authored-by: Yeswanth Surampudi  <yeswanth.sde@gmail.com>

Thanks again for unblocking this!