chore(deps): update rust crate prettyplease to v0.2.21 (#357)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [prettyplease](https://togithub.com/dtolnay/prettyplease) | workspace.dependencies | patch | `0.2.20` -> `0.2.21` |

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### Release Notes

<details>
<summary>dtolnay/prettyplease (prettyplease)</summary>

### [`v0.2.21`](https://togithub.com/dtolnay/prettyplease/releases/tag/0.2.21)

[Compare Source](https://togithub.com/dtolnay/prettyplease/compare/0.2.20...0.2.21)

-   Support formatting tail-call `become` expressions ([#&#8203;79](https://togithub.com/dtolnay/prettyplease/issues/79))

</details>

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