Bump the known_good_semver group with 1 update (#1802)

Bumps the known_good_semver group with 1 update:
[syn](https://github.com/dtolnay/syn).

<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>2.0.38</h2>
<ul>
<li>Fix <em>&quot;method 'peek' has an incompatible type for
trait&quot;</em> error when defining <code>bool</code> as a custom
keyword (<a
href="https://redirect.github.com/dtolnay/syn/issues/1518">#1518</a>,
thanks <a
href="https://github.com/Vanille-N"><code>@​Vanille-N</code></a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dtolnay/syn/commit/43632bfb6c78ee1f952645a268ab1ac4af162977"><code>43632bf</code></a>
Release 2.0.38</li>
<li><a
href="https://github.com/dtolnay/syn/commit/abd2c214b44da64a5e420d72919308300eebc23d"><code>abd2c21</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1518">#1518</a>
from Vanille-N/master</li>
<li><a
href="https://github.com/dtolnay/syn/commit/6701e6077e15013ef34b15e3ffdae2657e499d83"><code>6701e60</code></a>
Absolute path to <code>bool</code> in
<code>custom_punctuation.rs</code></li>
<li><a
href="https://github.com/dtolnay/syn/commit/7313d242398111423f046386aa0a75548f63d236"><code>7313d24</code></a>
Resolve single_match_else pedantic clippy lint in code generator</li>
<li><a
href="https://github.com/dtolnay/syn/commit/67ab64f3c09e17b23493c7cda498e7edb8830f21"><code>67ab64f</code></a>
Include unexpected token in the test failure message</li>
<li><a
href="https://github.com/dtolnay/syn/commit/137ae33486de3f2652487f8f64436ad1429df496"><code>137ae33</code></a>
Check no remaining token after the first literal</li>
<li><a
href="https://github.com/dtolnay/syn/commit/258e9e8a11d188c1ee1ffb2b069819239999f9ac"><code>258e9e8</code></a>
Ignore single_match_else pedantic clippy lint in test</li>
<li><a
href="https://github.com/dtolnay/syn/commit/92fd50ee8cb52968d9c66fbe6d67638c1f838e26"><code>92fd50e</code></a>
Test docs.rs documentation build in CI</li>
<li>See full diff in <a
href="https://github.com/dtolnay/syn/compare/2.0.37...2.0.38">compare
view</a></li>
</ul>
</details>
<br />


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