Handle correctly the enabling of the stop word with timer and TTS at the same time

[jlpouffier]

The stop word was enabled in two cases

• Long TTS
• Timer ring

And was disabled in two cases

• End of voice assistant process
• Timer ring end

The two use case where colliding when a timer was ringing while the voice assistant was running.

This PR adds a simple condition to prevent that from happening.

[github-actions[bot]]

Firmware built successfully! :tada:

Download and extract the firmware to install with https://web.esphome.io

Make sure to choose home-assistant-voice-esp32s3.factory.bin.