fix(disrupt_toggle_audit_syslog): tz=UTC in all datetime usage

[fruch]

seems like we are using naive datetime all of this nemesis, log output are in UTC time, we should align everything to work assuming it's UTC, to make sure times are aligned.

Ref: #7885

Testing

• [ ]

PR pre-checks (self review)

• [ ] I added the relevant backport labels
• [ ] I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)