Guest users can create new test cases

How it was found

Summary

According to the permission docs and test case docs , only user with a role Reporter or more is allowed to create a test case. This vulnerability allows, even Guest role users to create new test cases.

Steps to reproduce

1. Consider a private project with Guest role user.

2. Consider the API for creating an issue.

   The URL is https://gitlab.com/project_name/-/issues (POST).

   POST Data format for this is as follows:

   utf8=✓
   

authenticity_token= your_auth_token issue[title]=issue_title issue[description]=issue_description issue[confidential]=0 issue[issue_type]=issue issue[lock_version]=0

3. Now, in the parameter_set,  tamper with `issue[issue_type]` value and change it from `issue` to `test_case`.
4. Now, send the request.
5. A test case is now created. 

The test case can be viewed at https://gitlab.com/project_name/-/quality/test_cases

## Impact

Test Cases are important part of a project  as it helps product, quality and development teams to combine and Guest users should not be allowed to create it.