Do not render test cases with issues URL

Test cases can be rendered as regular issues that allow users to add comments and edit other attributes
that are not supposed to be changed. This raises another discussion: Maybe block not available attributes edit at model level to keep database consistent.

Steps to reproduce

1. Create any test case, for example https://gitlab.com/issue-reproduce/test-cases/-/quality/test_cases/2
2. Browse the test case using its iid on an issue URL, for example: https://gitlab.com/issue-reproduce/test-cases/-/issues/2

Possible solution

Redirect to TestCasesController#show when accessing a test case with a regular issue link.