(bugfix): replace create_event with send_event in PagerdutyNotifier

[bshea5]

Closes: #45626

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As noted in the most recent change log, https://airflow.apache.org/docs/apache-airflow-providers-pagerduty/stable/changelog.html, switch the create_event method to send_event. This PR fixes the provider as it still uses the prior method.

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[bshea5]

Covers issue #45630

[eladkal]

The fact that we didn't catch this when create_event was removed from the hook means that something is not working properly with the tests.
Merging to unblock the notifier but would be cool if someone has the time to look into the tests

[boring-cyborg]

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[potiuk]

The fact that we didn't catch this when create_event was removed from the hook means that something is not working properly with the tests. Merging to unblock the notifier but would be cool if someone has the time to look into the tests

.They were just mocking hook's methods not API methods. But the fact is that MyPy should detect it. For some reason it did not. The "self.hook" is clearly PagerdutyEventsHook and it does not have create_event so there should be no attr_defined or similar mypy error ... but you never know with MyPy. Sometimes it does not detect obvious things like that.

Potentially we could mock pdpyras.EventsAPISession(self.integration_key) session usage rather than hook usage and it would be detected in the tests.