docs: Update user-groups.mdx

[nimakarimi97]

removed 2 redundant words

Review Checklist

• [x] I have clicked on "allow edits by maintainers".
• [x] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [x] The correct base branch is being used, if not main
• [x] I have added tests to validate that the change in functionality is working as expected

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: nimakarimi97 / name: Nima Karimi (8a9cacaf89840808667b48e4631d3073feb7a513, 9fff8d638302e6345248528096437f26a683082f)

[willvedd]

@nimakarimi97 thanks for the contribution. Before we can merge you need to sign the CLA.

[nimakarimi97]

Hi @willvedd, I had forgotten to sign it. Done.