Update Rust crate serde to 1.0.208

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
serde (source)	dependencies	patch	1.0.207 -> 1.0.208

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Release Notes

serde-rs/serde (serde)

### [`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 ([#​2802](https://togithub.com/serde-rs/serde/issues/2802), thanks [@​jonhoo](https://togithub.com/jonhoo))

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Configuration

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