docs: fix numbering in middleware docs

[balazsorban44]

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

[styfle]

This is unnecessary since markdown will automatically increment

https://github.com/vercel/next.js/blob/canary/docs/advanced-features/middleware.md

https://spec.commonmark.org/dingus/?text=1.%20one%0A1.%20two%0A1.%20three%0A