chore(deps): update rust crate syn to v2.0.68 (#188)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [syn](https://togithub.com/dtolnay/syn) | workspace.dependencies | patch | `2.0.67` -> `2.0.68` |

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### Release Notes

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

### [`v2.0.68`](https://togithub.com/dtolnay/syn/releases/tag/2.0.68)

[Compare Source](https://togithub.com/dtolnay/syn/compare/2.0.67...2.0.68)

-   Improve panic location when `parse_quote!` parses invalid syntax ([#&#8203;1690](https://togithub.com/dtolnay/syn/issues/1690), thanks [@&#8203;stepancheg](https://togithub.com/stepancheg))
-   More efficient peek implementation for `Group` and `Lifetime` ([#&#8203;1687](https://togithub.com/dtolnay/syn/issues/1687))

</details>

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