User roles are duplicated when logging in/out

[flybot-nam-nguyenhoai]

Problem

When a user logs out and in again, their user roles are duplicated.

Steps to reproduce

1. Clone this repository.
2. Provide the necessary authentication files: oauth2.edn and admin.edn (see Configuration files).
3. Initialize the website for web development (see Front-end dev setup).
4. Log in to the website and check @re-frame.db/app-db in the ClojureScript REPL.
   The user (in :app/user) should contain roles like these (note the duplicate entries):

   [#:role{:name :editor,
           :date-granted #inst "2023-07-24T09:41:00.000-00:00"}
    #:role{:name :admin,
           :date-granted #inst "2023-07-24T09:41:00.000-00:00"}
    #:role{:name :editor,
           :date-granted #inst "2023-07-24T09:41:00.000-00:00"}
    #:role{:name :admin,
           :date-granted #inst "2023-07-24T09:41:00.000-00:00"}]

5. Log out and log in again n times, then check @re-frame.db/app-db in the ClojureScript REPL.
   The user should contain the same roles as above, duplicated exactly 2ⁿ more times.

Suggestion

Remove user roles before updating user information during login.