Fix reload in cert_expiry

[bdraco]

Proposed change

Switches async_listen_once to async_listen since its wrapped in entry.async_on_unload and the listener will fail to be removed on reload once the started event has fired because it was a one time listener (and already removed).

This could be refactored later to avoid calling the callable that async_listen_once returns once the started event has fired but that would add more complexity and since the started event is only fired once it doesn't have a performance penalty to use async_listen instead

fixes #95823

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[home-assistant]

Hey there @Cereal2nd, @jjlawren, mind taking a look at this pull request as it has been labeled with an integration (cert_expiry) you are listed as a code owner for? Thanks!

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[bdraco]

It was simple enough to change out so lets do it now. I think the risk is very low as I have a lot of these and was able to test before and after startup

[bdraco]

thanks 👍