Remove Forward Slashes from User Retention Tests

[caliskanugur]

Currently, slack reporter for recurring run fails with:

05:15:58.491 [31mERRO[0m[0114] error reporting: error with slack message post: 400 Bad Request 400: ****

The potential problem is: that it uses string manipulation to check the forward slashes. It sends the wrong parsed string to the slack API.

Example names (there are more, make sure to check names) that need updates: https://github.com/rancher/rancher/blob/release/v2.9/tests/v2/validation/auth/userretention/userretention_settings_test.go#L191-L193

Extra information about forward slashes in the test names: https://github.com/rancher/rancher/tree/main/tests#how-to-write-tests

[dasarinaidu]

rancher/rancher#47474