The group name you are trying to assign the role to is 'student-group'. Sentry allows granting roles to groups whose name is alphanumeric and the only special character allowed is an underscore (_). Because you have a hyphen (-). If there are any special characters apart from an underscore then you have to use backticks (`) as follows:
GRANT ROLE student TO GROUP `student-group`;
P.S.: It would have been better if you had shared the error log. It would have been easy to analyze.