Fix link to notifications and webhooks section

[h4de5]

Updated link to notifications documentation.

Summary

just a wrong link.

Related issue or discussion

the link to webhooks and notifications on:

https://docs.openwebui.com/ecosystem/computer/automate/scheduled-tasks/

leads to 404 error.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers