Bump proc-macro2 from 1.0.82 to 1.0.86 (#5638)

Bumps [proc-macro2](https://github.com/dtolnay/proc-macro2) from 1.0.82
to 1.0.86.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/dtolnay/proc-macro2/releases">proc-macro2's
releases</a>.</em></p>
<blockquote>
<h2>1.0.86</h2>
<ul>
<li>Documentation improvements</li>
</ul>
<h2>1.0.85</h2>
<ul>
<li>Mark some tests as only for 64-bit targets (<a
href="https://redirect.github.com/dtolnay/proc-macro2/issues/463">#463</a>)</li>
</ul>
<h2>1.0.84</h2>
<ul>
<li>Documentation improvements (<a
href="https://redirect.github.com/dtolnay/proc-macro2/issues/455">#455</a>,
thanks <a
href="https://github.com/CensoredUsername"><code>@​CensoredUsername</code></a>)</li>
</ul>
<h2>1.0.83</h2>
<ul>
<li>Optimize the representation of <code>Ident</code> (<a
href="https://redirect.github.com/dtolnay/proc-macro2/issues/462">#462</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.c...