Auto merge of #28902 - servo:dependabot/cargo/spin-0.9.4, r=jdm

Bump spin from 0.9.2 to 0.9.4

Bumps [spin](https://github.com/mvdnes/spin-rs) from 0.9.2 to 0.9.4.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/mvdnes/spin-rs/blob/master/CHANGELOG.md">spin's changelog</a>.</em></p>
<blockquote>
<h1>[0.9.4] - 2022-07-14</h1>
<h3>Fixed</h3>
<ul>
<li>Fixed unsoundness in <code>RwLock</code> on reader overflow</li>
<li>Relaxed <code>Send</code>/<code>Sync</code> bounds for <code>SpinMutex</code> and <code>TicketMutex</code> (doesn't affect <code>Mutex</code> itself)</li>
</ul>
<h1>[0.9.3] - 2022-04-17</h1>
<h3>Added</h3>
<ul>
<li>Implemented <code>Default</code> for <code>Once</code></li>
<li><code>Once::try_call_once</code></li>
</ul>
<h3>Fixed</h3>
<ul>
<li>Fixed bug that caused <code>Once::call_once</code> to incorrectly fail</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a href="https://github.com/mvdnes/spin-rs/commits">compare view</a></li>
</ul>
</details>
<br />

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Cargo.lock

@@ -6210,9 +6210,9 @@ checksum = "b72d540d5c565dbe1f891d7e21ceb21d2649508306782f1066989fccb0b363d3"
 
 [[package]]
 name = "spin"
-version = "0.9.2"
+version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "511254be0c5bcf062b019a6c89c01a664aa359ded62f78aa72c6fc137c0590e5"
+checksum = "7f6002a767bff9e83f8eeecf883ecb8011875a21ae8da43bffb817a57e78cc09"
 dependencies = [
  "lock_api 0.4.7",
 ]