build(deps): Bump hostname from 0.3.1 to 0.4.0 in /rust (#4620)

Bumps [hostname](https://github.com/svartalf/hostname) from 0.3.1 to
0.4.0.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/svartalf/hostname/blob/master/CHANGELOG.md">hostname's
changelog</a>.</em></p>
<blockquote>
<h2>[0.4.0] - 2024-04-01</h2>
<h3>Added</h3>
<ul>
<li>CI setup now covers almost all supported Tier 1 and Tier 2 platform
targets</li>
</ul>
<h3>Changed</h3>
<ul>
<li>Minimum Supported Rust version set to <code>1.67.0</code></li>
<li>Rust edition set to &quot;2021&quot;</li>
</ul>
<h3>Fixed</h3>
<ul>
<li>Handle edge cases for POSIX systems (<a
href="https://redirect.github.com/svartalf/hostname/issues/14">#14</a>)</li>
<li>docs.rs documentation build</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="0e311b92ea"><code>0e311b9</code></a>
Release v0.4.0</li>
<li><a
href="e96d1fde34"><code>e96d1fd</code></a>
Updating the repo to make it usable again</li>
<li><a
href="ecf28ebbf4"><code>ecf28eb</code></a>
bump version-sync: 0.8 -&gt; 0.9 (<a
href="https://redirect.github.com/svartalf/hostname/issues/17">#17</a>)</li>
<li><a
href="4a178ed8f4"><code>4a178ed</code></a>
Handle posix hostname edge cases (<a
href="https://redirect.github.com/svartalf/hostname/issues/14">#14</a>)</li>
<li><a
href="7e930e9aca"><code>7e930e9</code></a>
Upgrade rust edition and migrate dependices（cfg_if, windows_rs） (<a
href="https://redirect.github.com/svartalf/hostname/issues/18">#18</a>)</li>
<li>See full diff in <a
href="https://github.com/svartalf/hostname/compare/v0.3.1...v0.4.0">compare
view</a></li>
</ul>
</details>
<br />


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rust/Cargo.lock

@@ -1899,7 +1899,7 @@ dependencies = [
  "futures",
  "git-version",
  "hex",
- "hostname 0.3.1",
+ "hostname 0.4.0",
  "ipconfig",
  "keyring",
  "minidumper",

rust/gui-client/src-tauri/Cargo.toml

@@ -24,7 +24,7 @@ firezone-headless-client = { path = "../../headless-client" }
 git-version = "0.3.9"
 hex = "0.4.3"
 # Same crate Hickory uses
-hostname = "0.3.1"
+hostname = "0.4.0"
 keyring = "2.3.2"
 minidumper = "0.8.2"
 native-dialog = "0.7.0"