Fix Airflow V2 incompatibility in ExternalTaskSensor

[fuatcakici]

The parameter in WorkflowTrigger is "execution_dates", and not "execution_date"

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[Copilot]

Pull Request Overview

This PR corrects the parameter name passed to WorkflowTrigger in ExternalTaskSensor.execute, ensuring the key matches the expected “execution_dates” signature.

• Changed the dict key from "execution_date" to "execution_dates" when not running Airflow v3.0+
• Aligns sensor payload with the trigger’s parameter name

[shahar1]

@fuatcakici Welcome to Apache Airflow! This is a great catch :)
I hope that you will excuse me, but I took over the PR to add some tests so we'd be able to track such errors for the next times.
While adding the tests, I've found another related bug which I fixed on the way - I tagged the relevant commiters for their review.
Thanks for your contribution!

[fuatcakici]

@shahar1 of course, by all means!

I had also noticed the other bug by the way, as in the DagRun object not having the run_after parameter, but I did not see it raising any errors so I just assumed that I was overlooking something, so I'm glad to see it actually 😄

In any case, thanks for being so proactive!

[kaxil]

@shahar1 We should update the PR title now to match the bug fix