Bumps the known_good_semver group with 3 updates:
[log](https://github.com/rust-lang/log),
[syn](https://github.com/dtolnay/syn) and
[clap](https://github.com/clap-rs/clap).

Updates `log` from 0.4.20 to 0.4.21
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/rust-lang/log/blob/master/CHANGELOG.md">log's
changelog</a>.</em></p>
<blockquote>
<h2>[0.4.21] - 2024-02-27</h2>
<h2>What's Changed</h2>
<ul>
<li>Minor clippy nits by <a
href="https://github.com/nyurik"><code>@​nyurik</code></a> in <a
href="https://redirect.github.com/rust-lang/log/pull/578">rust-lang/log#578</a></li>
<li>Simplify Display impl by <a
href="https://github.com/nyurik"><code>@​nyurik</code></a> in <a
href="https://redirect.github.com/rust-lang/log/pull/579">rust-lang/log#579</a></li>
<li>Set all crates to 2021 edition by <a
href="https://github.com/nyurik"><code>@​nyurik</code></a> in <a
href="https://redirect.github.com/rust-lang/log/pul...