fix(admin): correct an to and in restore documentation

[JRehkemper]

The restore documentation seems to contain a typo. I corrected it by changing 'an' to 'and'.

☑️ Resolves

No Upstream issue

🖼️ Screenshots

✅ Checklist

• I have built the documentation locally and reviewed the output
• Screenshots are included for visual changes
• I have not moved or renamed pages (or added a redirect if I did)
• I have run codespell or similar and addressed any spelling issues

[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/documentation/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

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