deps: update rust crate serde to v1.0.208 (#218)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [serde](https://serde.rs)
([source](https://togithub.com/serde-rs/serde)) | dependencies | patch |
`1.0.207` -> `1.0.208` |

---

### Release Notes

<details>
<summary>serde-rs/serde (serde)</summary>

###
[`v1.0.208`](https://togithub.com/serde-rs/serde/releases/tag/v1.0.208)

[Compare
Source](https://togithub.com/serde-rs/serde/compare/v1.0.207...v1.0.208)

- Support serializing and deserializing unit structs in a `flatten`
field ([#&#8203;2802](https://togithub.com/serde-rs/serde/issues/2802),
thanks [@&#8203;jonhoo](https://togithub.com/jonhoo))

</details>

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