[FIX] Desktop notifications not displayed when agent has not focussed the browser

[renatobecker-zz]

@RocketChat/core

Closes #10074

This PR fixes the bug related to desktop notifications in LiveChat rooms. When a visitor was sending messages and the agent was not focused on the browser, desktop notifications were not displayed to the agent.

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✅ renatobecker
❌ Renato Becker

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