Update dependencies (#27)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [proc-macro2](https://togithub.com/dtolnay/proc-macro2) |
workspace.dependencies | patch | `1.0.85` -> `1.0.86` |
| [syn](https://togithub.com/dtolnay/syn) | workspace.dependencies |
patch | `2.0.66` -> `2.0.68` |

---

### Release Notes

<details>
<summary>dtolnay/proc-macro2 (proc-macro2)</summary>

###
[`v1.0.86`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.86)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.85...1.0.86)

-   Documentation improvements

</details>

<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))

### [`v2.0.67`](https://togithub.com/dtolnay/syn/releases/tag/2.0.67)

[Compare
Source](https://togithub.com/dtolnay/syn/compare/2.0.66...2.0.67)

- Produce more accurate error message locations for errors located at
the end of a nested group
([#&#8203;1679](https://togithub.com/dtolnay/syn/issues/1679),
[#&#8203;1680](https://togithub.com/dtolnay/syn/issues/1680))
- Support peeking `LitCStr` in ParseStream::peek
([#&#8203;1682](https://togithub.com/dtolnay/syn/issues/1682))

</details>

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