chore(deps): update rust crate syn to v2.0.64 (#468)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [syn](https://togithub.com/dtolnay/syn) | workspace.dependencies |
patch | `2.0.63` -> `2.0.64` |

---

### Release Notes

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

### [`v2.0.64`](https://togithub.com/dtolnay/syn/releases/tag/2.0.64)

[Compare
Source](https://togithub.com/dtolnay/syn/compare/2.0.63...2.0.64)

- Support using ParseBuffer across `catch_unwind`
([#&#8203;1646](https://togithub.com/dtolnay/syn/issues/1646))
- Validate that the expression in a let-else ends in brace as required
by rustc ([#&#8203;1648](https://togithub.com/dtolnay/syn/issues/1648),
[#&#8203;1649](https://togithub.com/dtolnay/syn/issues/1649))
- Legalize invalid const generic arguments by wrapping in braces
([#&#8203;1654](https://togithub.com/dtolnay/syn/issues/1654),
[#&#8203;1655](https://togithub.com/dtolnay/syn/issues/1655))
- Fix some expression precedence edge cases involving `break` and
`return` in loop headers
([#&#8203;1656](https://togithub.com/dtolnay/syn/issues/1656))
- Always print closure bodies with a brace when the closure has an
explicit return type
([#&#8203;1658](https://togithub.com/dtolnay/syn/issues/1658))
- Automatically insert necessary parentheses in ToTokens for Expr when
required by expression precedence
([#&#8203;1659](https://togithub.com/dtolnay/syn/issues/1659))
- Support struct literal syntax in match guard expressions
([#&#8203;1662](https://togithub.com/dtolnay/syn/issues/1662))

</details>

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