deps: update rust crate serde to v1.0.209 (#222)

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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 |
`1.0.208` -> `1.0.209` |

---

### Release Notes

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

###
[`v1.0.209`](https://togithub.com/serde-rs/serde/releases/tag/v1.0.209)

[Compare
Source](https://togithub.com/serde-rs/serde/compare/v1.0.208...v1.0.209)

- Fix deserialization of empty structs and empty tuples inside of
untagged enums
([#&#8203;2805](https://togithub.com/serde-rs/serde/issues/2805), thanks
[@&#8203;Mingun](https://togithub.com/Mingun))

</details>

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