Ensure role exists before we try to remove the role assignment

[rdimitrov]

Summary

The following PR adds an additional check caught by the smoke test where Minder returned a positive response in case there was no existing role assignment and we tried to remove it.

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

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Attach screenshots if helpful.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 54.303% (+0.001%) from 54.302%
when pulling 2b69e3d on check-role-exists
into b5f9c96 on main.