Describe the Bug

Description
Opening a relationship field filter in the list view and switching the operator from equals to is in causes duplicate options to appear in the value dropdown

Link to the code that reproduces this issue

https://github.com/zubricks/where-builder-repro

Reproduction Steps

1. Go to the Products list view → open a filter → select the category field with equals operator → select a value
2. Change the operator to is in
3. Open the value dropdown — duplicate entries appear

Which area(s) are affected?

area: core

Environment Info

Binaries:
  Node: 23.11.0
  npm: 11.4.2
  Yarn: N/A
  pnpm: 10.10.0
Relevant Packages:
  payload: 3.79.0
  next: 15.4.11
  @payloadcms/db-postgres: 3.79.0
  @payloadcms/drizzle: 3.79.0
  @payloadcms/graphql: 3.79.0
  @payloadcms/next/utilities: 3.79.0
  @payloadcms/richtext-lexical: 3.79.0
  @payloadcms/translations: 3.79.0
  @payloadcms/ui/shared: 3.79.0
  react: 19.2.1
  react-dom: 19.2.1