Fix small typo in docs

[mendelgordon]

Fix typo in magic session docs (be - been)

What does this PR do?

Fix typo in magic session docs (be - been)
(Update create-magic-url-session.md)

Test Plan

N/A

Related PRs and Issues

N/A

Checklist

• [ ✅ ] Have you read the Contributing Guidelines on issues?
• [ N/A ] If the PR includes a change to an API's metadata (desc, label, params, etc.), does it also include updated API specs and example docs?

[eldadfux]

@mendelgordon thank you!