Draft: Enhance secret push protection related specs
What does this MR do and why?
This merge request updates the secret push protection-related specs to improve their structure, and ensure the feature works as intended following the move to scan delta changes (diffs) instead of entire files in !158984 (merged).
It also introduces a slight UX update when displaying secrets found when they couldn't be associated with a commit.
MR acceptance checklist
I have evaluated this MR against the MR acceptance checklist.