Bumps the known_good_semver group with 1 update:
[serde_json](https://github.com/serde-rs/json).

Updates `serde_json` from 1.0.120 to 1.0.121
<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>v1.0.121</h2>
<ul>
<li>Optimize position search in error path (<a
href="https://redirect.github.com/serde-rs/json/issues/1160">#1160</a>,
thanks <a
href="https://github.com/purplesyringa"><code>@​purplesyringa</code></a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/serde-rs/json/commit/eca2658a22cb39952783cb6914eb18242659f66a"><code>eca2658</code></a>
Release 1.0.121</li>
<li><a
href="https://github.com/serde-rs/json/commit/b0d678cfb473386830d559b6ab255d9e21ba39c5"><code>b0d678c</code></a>
Merge pull request <a
href="https://redirect.github.com/serde-rs/json/issues/1160">#1160</a>
from iex-rs/efficient-position</li>
<li><a
href="https://github.com/serde-rs/json/commit/b1edc7d13f72880fd0ac569403a409e5f7961d5f"><code>b1edc7d</code></a>
Optimize position search in error path</li>
<li><a
href="https://github.com/serde-rs/json/commit/40dd7f5e862436f02471fe076f3486c55e472bc2"><code>40dd7f5</code></a>
Merge pull request <a
href="https://redirect.github.com/serde-rs/json/issues/1159">#1159</a>
from iex-rs/fix-recursion</li>
<li><a
href="https://github.com/serde-rs/json/commit/6a306e6ee9f47f3b37088217ffe3ebe9bbb54e5a"><code>6a306e6</code></a>
Move call to tri! out of check_recursion!</li>
<li><a
href="https://github.com/serde-rs/json/commit/3f1c6de4af28b1f6c5100da323f2bffaf7c2083f"><code>3f1c6de</code></a>
Ignore byte_char_slices clippy lint in test</li>
<li><a
href="https://github.com/serde-rs/json/commit/3fd6f5f49dc1c732d9b1d7dfece4f02c0d440d39"><code>3fd6f5f</code></a>
Merge pull request <a
href="https://redirect.github.com/serde-rs/json/issues/1153">#1153</a>
from dpathakj/master</li>
<li><a
href="https://github.com/serde-rs/json/commit/fcb5e83e44abe0f9c27c755a240a6ad56312c090"><code>fcb5e83</code></a>
Correct documentation URL for Value's Index impl.</li>
<li>See full diff in <a
href="https://github.com/serde-rs/json/compare/v1.0.120...v1.0.121">compare
view</a></li>
</ul>
</details>
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