persistent prompt in DTS

[WiktorG351]

The problem you're addressing (if any)

Right now the prompt in DTS is based on the bash version:

bash-5.1#

This might become troublesome in the future, if we have tests that rely on looking for that specific string in the terminal.

Describe the solution you'd like

A unified prompt that always looks the same, regardless of bash version.

Where is the value to a user, and who might that user be?

Tests wouldn't have to use regexp to set prompt, it would be a direct match

Describe alternatives you've considered

No response

Additional context

https://github.com/Dasharo/open-source-firmware-validation/pull/267#discussion_r1570431312