Update Rust crate serde to v1.0.209 (#1401)

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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)) | workspace.dependencies
| patch | `1.0.204` -> `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))

###
[`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))

###
[`v1.0.207`](https://togithub.com/serde-rs/serde/releases/tag/v1.0.207)

[Compare
Source](https://togithub.com/serde-rs/serde/compare/v1.0.206...v1.0.207)

- Improve interactions between `flatten` attribute and
`skip_serializing`/`skip_deserializing`
([#&#8203;2795](https://togithub.com/serde-rs/serde/issues/2795), thanks
[@&#8203;Mingun](https://togithub.com/Mingun))

###
[`v1.0.206`](https://togithub.com/serde-rs/serde/releases/tag/v1.0.206)

[Compare
Source](https://togithub.com/serde-rs/serde/compare/v1.0.205...v1.0.206)

- Improve support for `flatten` attribute inside of enums
([#&#8203;2567](https://togithub.com/serde-rs/serde/issues/2567), thanks
[@&#8203;Mingun](https://togithub.com/Mingun))

###
[`v1.0.205`](https://togithub.com/serde-rs/serde/releases/tag/v1.0.205)

[Compare
Source](https://togithub.com/serde-rs/serde/compare/v1.0.204...v1.0.205)

- Use serialize_entry instead of serialize_key + serialize_value when
serialize flattened newtype enum variants
([#&#8203;2785](https://togithub.com/serde-rs/serde/issues/2785), thanks
[@&#8203;Mingun](https://togithub.com/Mingun))
- Avoid triggering a collection_is_never_read lint in the
deserialization of enums containing flattened fields
([#&#8203;2791](https://togithub.com/serde-rs/serde/issues/2791))

</details>

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