Bump enumn from 0.1.12 to 0.1.13 (#5061)

Bumps [enumn](https://github.com/dtolnay/enumn) from 0.1.12 to 0.1.13.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/dtolnay/enumn/releases">enumn's
releases</a>.</em></p>
<blockquote>
<h2>0.1.13</h2>
<ul>
<li>Update proc-macro2 to fix caching issue when using a rustc-wrapper
such as sccache</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dtolnay/enumn/commit/de964e3ce0463f01dabb94c168d507254facfb86"><code>de964e3</code></a>
Release 0.1.13</li>
<li><a
href="https://github.com/dtolnay/enumn/commit/52dcafcb2ee193be8839dc0f96bfa0e151888645"><code>52dcafc</code></a>
Pull in proc-macro2 sccache fix</li>
<li><a
href="https://github.com/dtolnay/enumn/commit/ba2e288a83c5e62d1e29b993523ccf0528043ab0"><code>ba2e288</code></a>
Test docs.rs documentation build in CI</li>
<li><a
href="https://github.com/dtolnay/enumn/commit/6f5a37e5a9dcdb75987552b44d7ebdbd7f0a2a93"><code>6...