The Internal supplier request is a one-time process. Once the project owner of the supplier request submits the request, it can be edited till the request is in Pending Approval status. Based on the question, looks like the intent is to not create the supplier in SLP.
1. Either let the supplier request in the Pending Approval status forever;
2. Approver can Deny the request which moves it to DENIED status.
Either of the options will ensure that no supplier 360 will be created.
A cancel options ( one that is available in Supplier Registration Projects) does not exist in Supplier Request project.