Bump armeria-junit5 from 1.20.3 to 1.21.0 (#7465)

Bumps [armeria-junit5](https://github.com/line/armeria) from 1.20.3 to
1.21.0.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/line/armeria/releases">armeria-junit5's
releases</a>.</em></p>
<blockquote>
<h2>armeria-1.21.0</h2>
<p>See <a href="https://armeria.dev/release-notes/1.21.0/">the release
notes</a> for the complete change list.</p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="a2de8291b1"><code>a2de829</code></a>
Release armeria-1.21.0</li>
<li><a
href="684329f5ee"><code>684329f</code></a>
Update to use JDK 19 when releasing</li>
<li><a
href="fbc45b3a39"><code>fbc45b3</code></a>
Update the project version to 1.21.1-SNAPSHOT</li>
<li><a
href="d18f029a72"><code>d18f029</code></a>
Add release note for 1.21.0 and 1.16.1 (<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4581">#4581</a>)</li>
<li><a
href="3a23bffac4"><code>3a23bff</code></a>
Update dependencies (<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4579">#4579</a>)</li>
<li><a
href="2ff218bae2"><code>2ff218b</code></a>
build with jdk 19 and Gradle 7.6 (<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4466">#4466</a>)</li>
<li><a
href="5d92b30a73"><code>5d92b30</code></a>
<code>Flags#meterRegistry</code> returns a <code>MeterRegistry</code>
(<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4580">#4580</a>)</li>
<li><a
href="dd49448e73"><code>dd49448</code></a>
Limit the max length of decoded content in
<code>Decoding{Service,Client}</code> (<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4564">#4564</a>)</li>
<li><a
href="fee87f8da9"><code>fee87f8</code></a>
Add client and server default headers (<a
href="https://github-redirect.dependabot.com/line/armeria/issues/4520">#4520</a>)</li>
<li><a
href="f4781d52a3"><code>f4781d5</code></a>
Fix a deadlock when a late response are written first in HTTP/1
pipelining (#...</li>
<li>Additional commits viewable in <a
href="https://github.com/line/armeria/compare/armeria-1.20.3...armeria-1.21.0">compare
view</a></li>
</ul>
</details>
<br />


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testing/armeria-shaded-for-testing/build.gradle.kts

@@ -5,7 +5,7 @@ plugins {
 }
 
 dependencies {
-  implementation("com.linecorp.armeria:armeria-junit5:1.20.3")
+  implementation("com.linecorp.armeria:armeria-junit5:1.21.0")
 }
 
 tasks {