Fix typo in features.md for URL management section

[1sh-repalto]

Fixed typo from "where" to "were" in the sentence:
"Plone has an integrated mechanism to remember URLs that were modified".

• I have granted permission to publish my contribution according to Granting permission to publish.
  Minor typographical corrections and other contributions that are not "material in nature" are exempt from this requirement.
• I followed the guidelines in Contributing to Plone Training.
• I verified there aren't any other open pull requests for the same change.
• I successfully built the documentation and ran quality checks on my changes locally according to Building and Checking the Quality of Documentation.
• If needed, I added new terms to the Glossary file glossary.md and referenced them in the documentation. Note that terms that are defined in external Sphinx documentation, including Plone 6 documentation, may be referenced with a {term} directive without adding the definition to the local glossary.md file.

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I, Vansh Negi, agree to have this contribution published under Creative Commons 4.0 International License (CC BY 4.0), with attribution to the Plone Foundation.

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📚 Documentation preview 📚: https://plone-training--989.org.readthedocs.build/

[stevepiercy]

Thank you!