Bump thiserror from 1.0.41 to 1.0.43 in /cmd/pinniped-proxy (#6432)

Bumps [thiserror](https://github.com/dtolnay/thiserror) from 1.0.41 to
1.0.43.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/dtolnay/thiserror/releases">thiserror's
releases</a>.</em></p>
<blockquote>
<h2>1.0.42</h2>
<ul>
<li>Fix compile error in derived Display impl if there was a nonstandard
<code>write!</code> macro in scope (<a
href="https://redirect.github.com/dtolnay/thiserror/issues/239">#239</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dtolnay/thiserror/commit/225adab854715459bc81dd3e788805debcf7f310"><code>225adab</code></a>
Release 1.0.43</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/f6dc5e54e2c0604388ac43da99ebea5e9c75decc"><code>f6dc5e5</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/thiserror/issues/242">#242</a>
from dtolnay/stdwrite</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/cab9fec03e0f734ab7d42aa5de34024d0df761cd"><code>cab9fec</code></a>
Avoid calling a nonstandard write! macro that might be in scope</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/900f0189889133f1d76365dc961023f85e4b3a19"><code>900f018</code></a>
Revert &quot;Avoid calling a nonstandard write! macro that might be in
scope&quot;</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/305be4a9798449ef757b8c9ddd2a6c3f6a10a101"><code>305be4a</code></a>
Release 1.0.42</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/6165f5859661500fe47a796bca73bac5504f90e3"><code>6165f58</code></a>
Merge pull request <a
href="https://redirect.github.com/dtolnay/thiserror/issues/240">#240</a>
from dtolnay/stdwrite</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/264b7d19360332bd2cf8289a54619c3360a2f8fe"><code>264b7d1</code></a>
Avoid calling a nonstandard write! macro that might be in scope</li>
<li><a
href="https://github.com/dtolnay/thiserror/commit/43f3a2a661f1fa75a23933a0d039677307a4e1e0"><code>43f3a2a</code></a>
Update to 2021 edition</li>
<li>See full diff in <a
href="https://github.com/dtolnay/thiserror/compare/1.0.41...1.0.43">compare
view</a></li>
</ul>
</details>
<br />


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