chore(deps): bump syn from 2.0.106 to 2.0.108 (#18291)

Bumps [syn](https://github.com/dtolnay/syn) from 2.0.106 to 2.0.108.
<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>2.0.108</h2>
<ul>
<li>Parse unrecognized or invalid literals as Lit::Verbatim (<a
href="https://redirect.github.com/dtolnay/syn/issues/1925">#1925</a>)</li>
</ul>
<h2>2.0.107</h2>
<ul>
<li>Improve panic message when constructing a LitInt, LitFloat, or Lit
from invalid syntax (<a
href="https://redirect.github.com/dtolnay/syn/issues/1917">#1917</a>)</li>
<li>Improve panic message on Punctuated index out of bounds (<a
href="https://redirect.github.com/dtolnay/syn/issues/1922">#1922</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dtolnay/syn/commit/7a7e331255822d49bea01e29c326ee7a5cd5415c"><code>7a7e331</code></a>
Release 2.0.108</li>
<li><a
href="https://github.com/dtolnay/syn/commit/30463afa201abc30e086bd1fb1deb714eb8910f4"><code>30463af</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1926">#1926</a>
from dtolnay/litfuzz</li>
<li><a
href="https://github.com/dtolnay/syn/commit/1cc9167f60d209865e91bf73a949d25914e6bf18"><code>1cc9167</code></a>
Add fuzzer for literal parsing</li>
<li><a
href="https://github.com/dtolnay/syn/commit/c49e1d3a65ab423beee54ed730ea3f849ec49e0b"><code>c49e1d3</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1925">#1925</a>
from dtolnay/litparse</li>
<li><a
href="https://github.com/dtolnay/syn/commit/d047536103b7edfb0408dab8ec65cde19e73a88f"><code>d047536</code></a>
Report unexpected verbatim literals in test</li>
<li><a
href="https://github.com/dtolnay/syn/commit/ce9776747974555e30cd890b9e1d3030e02efc13"><code>ce97767</code></a>
Parse unrecognized or invalid literals as Lit::Verbatim</li>
<li><a
href="https://github.com/dtolnay/syn/commit/e4a8957feb1b86e6da4309c9886ca15ddfd7b7ad"><code>e4a8957</code></a>
Release 2.0.107</li>
<li><a
href="https://github.com/dtolnay/syn/commit/1792e83acfcc4810ccca70c22952986a6ea09d7e"><code>1792e83</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/syn/issues/1922">#1922</a>
from dtolnay/outofbounds</li>
<li><a
href="https://github.com/dtolnay/syn/commit/532e4af53355f8c4585251e1507336bed8d39f14"><code>532e4af</code></a>
Improve panic message on Punctuated index out of bounds</li>
<li><a
href="https://github.com/dtolnay/syn/commit/909c2221dd582e18f748988384e8ec4edd7544cf"><code>909c222</code></a>
Add test of Punctuated indexing</li>
<li>Additional commits viewable in <a
href="https://github.com/dtolnay/syn/compare/2.0.106...2.0.108">compare
view</a></li>
</ul>
</details>
<br />


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