[pentest] Add registers to clobber list in assembly snippets

[nasahlpa]

Description

The pentests use different ASm based snippets that we use for the FI and SCA evaluation. We should extend the ASM snippets by adding the registers those snippets are modfying to the clobber list. That prevents that the compiler is aware of those changes.

[nasahlpa]

See #28993 for more details.