chore(deps): update dependency knip to v5.21.0 (#303)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [knip](https://knip.dev)
([source](https://togithub.com/webpro-nl/knip/tree/HEAD/packages/knip))
| [`5.20.0` ->
`5.21.0`](https://renovatebot.com/diffs/npm/knip/5.20.0/5.21.0) |
[![age](https://developer.mend.io/api/mc/badges/age/npm/knip/5.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/knip/5.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/knip/5.20.0/5.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/knip/5.20.0/5.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>webpro-nl/knip (knip)</summary>

### [`v5.21.0`](https://togithub.com/webpro-nl/knip/releases/tag/5.21.0)

[Compare
Source](https://togithub.com/webpro-nl/knip/compare/5.20.0...5.21.0)

- Add webdriver-io plugin
([`7414dc1`](https://togithub.com/webpro-nl/knip/commit/7414dc1a))
- Update plugin docs
([`df35b9f`](https://togithub.com/webpro-nl/knip/commit/df35b9f4))
- Minor housekeeping
([`1422c9d`](https://togithub.com/webpro-nl/knip/commit/1422c9d2))
- Add size-limit plugin
([`dbd82f8`](https://togithub.com/webpro-nl/knip/commit/dbd82f87))
- Add lockfile-lint plugin
([`d70d0de`](https://togithub.com/webpro-nl/knip/commit/d70d0de7))
- Use provided name in plugin template
([`43961f9`](https://togithub.com/webpro-nl/knip/commit/43961f91))
- Minor housekeeping
([`c81b1a2`](https://togithub.com/webpro-nl/knip/commit/c81b1a23))
- Update readme with badges and stuff
([`c18fcba`](https://togithub.com/webpro-nl/knip/commit/c18fcba5))
- Update docs (Configuring Project Files)
([`e10ac2e`](https://togithub.com/webpro-nl/knip/commit/e10ac2e4))

</details>

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