Bump serde_json from 1.0.99 to 1.0.100 in /cmd/pinniped-proxy (#6409)

Bumps [serde_json](https://github.com/serde-rs/json) from 1.0.99 to
1.0.100.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/serde-rs/json/releases">serde_json's
releases</a>.</em></p>
<blockquote>
<h2>v1.0.100</h2>
<ul>
<li>Support <code>-Z minimal-versions</code></li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/serde-rs/json/commit/d2fce19685bf0e3d493a9d785665137654c79e6d"><code>d2fce19</code></a>
Release 1.0.100</li>
<li><a
href="https://github.com/serde-rs/json/commit/897f913dd234c8cd0810fc0689d76a146aaec4ad"><code>897f913</code></a>
No pre_ci in this repo</li>
<li><a
href="https://github.com/serde-rs/json/commit/8f8a2b1c47ebe4193b3a0b06805f31619e4c1cf8"><code>8f8a2b1</code></a>
Eliminate syn 1 from minimal-versions</li>
<li><a
href="https://github.com/serde-rs/json/commit/f482ed3d3662446914221d8c0a1efe3d7ffe8f82"><code>f482ed3</code></a>
Add CI job using minimal-versions</li>
<li><a
href="https://github.com/serde-rs/json/commit/79caf276312947b502df0b905c117f76557edc61"><code>79caf27</code></a>
Sort Cargo.toml dependencies list</li>
<li><a
href="https://github.com/serde-rs/json/commit/e98e664b42aceb245eaf801fc9ab726284693a68"><code>e98e664</code></a>
Resolve explicit_iter_loop pedantic clippy lint</li>
<li><a
href="https://github.com/serde-rs/json/commit/fdb7800f5aa2870ffa87712dac417883daac3656"><code>fdb7800</code></a>
Support a manual trigger on CI workflow</li>
<li>See full diff in <a
href="https://github.com/serde-rs/json/compare/v1.0.99...v1.0.100">compare
view</a></li>
</ul>
</details>
<br />


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