Change list_secrets to use async await

[Lucioric2000]

The list_secrets call returns a coroutine that should be awaited, therefore, I am introducing the await instruction, which was absent, to the async secrets getter example.

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Fixes #<issue_number_goes_here> 🦕

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[gemini-code-assist]

Code Review

This pull request updates the asynchronous sample for listing secrets in the Google Cloud Secret Manager by adding the missing await keyword to the list_secrets method call. This ensures the asynchronous request is properly executed within the async function. I have no feedback to provide.