Bump syn from 2.0.66 to 2.0.67 (#2421)

Bumps [syn](https://github.com/dtolnay/syn) from 2.0.66 to 2.0.67.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/dtolnay/syn/releases">syn's
releases</a>.</em></p>
<blockquote>
<h2>2.0.67</h2>
<ul>
<li>Produce more accurate error message locations for errors located at
the end of a nested group (<a
href="https://redirect.github.com/dtolnay/syn/issues/1679">#1679</a>, <a
href="https://redirect.github.com/dtolnay/syn/issues/1680">#1680</a>)</li>
<li>Support peeking <code>LitCStr</code> in ParseStream::peek (<a
href="https://redirect.github.com/dtolnay/syn/issues/1682">#1682</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dtolnay/syn/commit/25f6299c982276bf55faac834538d78ea61d6bad"><code>25f6299</code></a>
Release 2.0.67</li>
<li><a
href="https://github.com/dtolnay/syn/commit/666e15e95ff3763571f14af93be2641eecc5c2d9"><code>666e15e</code></a>
Revert &quot;List peekable token types in documentation of Peek
trait&quot;</li>
<li><a
href="https://github.com/dtolnay/syn/commit/2955706a736b5ca293eff45a3b2cade32baa01aa"><code>2955706</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1683">#1683</a>
from dtolnay/peekimpl</li>
<li><a
href="https://github.com/dtolnay/syn/commit/0c902919850353ddfe4d90f5ba0474e6ac8aaaa8"><code>0c90291</code></a>
List peekable token types in documentation of Peek trait</li>
<li><a
href="https://github.com/dtolnay/syn/commit/26ce3d9134644b62298963d0abf0e9a3584f6896"><code>26ce3d9</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1682">#1682</a>
from dtolnay/peekcstr</li>
<li><a
href="https://github.com/dtolnay/syn/commit/ec0c84b282c8ade12f6afaad7425b90ec5a1fd7d"><code>ec0c84b</code></a>
Make LitCStr peekable</li>
<li><a
href="https://github.com/dtolnay/syn/commit/8cb56cc59d8ea0117dd6df3915f4c730249618bc"><code>8cb56cc</code></a>
Update test suite to nightly-2024-06-20</li>
<li><a
href="https://github.com/dtolnay/syn/commit/7cc7eac262467d4c1e6cac8f9beeb20d256f7d49"><code>7cc7eac</code></a>
Inline lookahead::is_delimiter into delimiter Token impls</li>
<li><a
href="https://github.com/dtolnay/syn/commit/8a2a86bce92d1f440a7b2d6d244ab825d426bb61"><code>8a2a86b</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1681">#1681</a>
from dtolnay/offset</li>
<li><a
href="https://github.com/dtolnay/syn/commit/e86538ccd80494c8bf239b36550c0f9e298b50c5"><code>e86538c</code></a>
Optimize reverse iteration of TokenBuffer</li>
<li>Additional commits viewable in <a
href="https://github.com/dtolnay/syn/compare/2.0.66...2.0.67">compare
view</a></li>
</ul>
</details>
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