Hello @jikolji
Thanks for posting this in the global Canvas Community!
I know this is not the answer you are looking for, but I don't think there is a way to restrict teachers from regrading quiz submissions in speedgrader, without revoking their all of their permissions to edit and enter all grades in the course.
I looked at the Canvas permissions page. I saw that there is a permission called Grades - Edit. This permission is responsible for Allowing users to edit grades and add comments in SpeedGrader as well as some other additional considerations. I don't think this would be something you would want to restrict, but the option is there, if needed. This is usually restricted for course roles such as students, observers, or designers.
There doesn't appear to be a permissions that would restrict them from regrading questions that were automatically graded in quizzes, unfortunately.
-Colton