Bump org.checkerframework:checker-qual from 4.2.0 to 4.2.1 in the dependencies group

Bumps the dependencies group with 1 update: [org.checkerframework:checker-qual](https://github.com/typetools/checker-framework).

Updates `org.checkerframework:checker-qual` from 4.2.0 to 4.2.1
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/typetools/checker-framework/releases">org.checkerframework:checker-qual's releases</a>.</em></p>
<blockquote>
<h2>Checker Framework 4.2.1</h2>
<h2>Version 4.2.1 (2026-07-01)</h2>
<h3>Closed issues</h3>
<p><a href="https://redirect.github.com/typetools/checker-framework/issues/7726">#7726</a>.</p>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/typetools/checker-framework/blob/master/docs/CHANGELOG.md">org.checkerframework:checker-qual's changelog</a>.</em></p>
<blockquote>
<h2>Version 4.2.1 (2026-07-01)</h2>
<h3>Closed issues</h3>
<p><a href="https://redirect.github.com/typetools/checker-framework/issues/7726">#7726</a>.</p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/typetools/checker-framework/commit/ef8cecd00663136e5bb4d6d3d32f936d500f519c"><code>ef8cecd</code></a> new release 4.2.1</li>
<li><a href="https://github.com/typetools/checker-framework/commit/5d046116bece9b5ebb359fab260c2d17988a5e41"><code>5d04611</code></a> Prep for release.</li>
<li><a href="https://github.com/typetools/checker-framework/commit/0907ddc90cd25f32e5bf8922d8277d0b41de7fc2"><code>0907ddc</code></a> Use <code>@MonotonicNonNull</code></li>
<li><a href="https://github.com/typetools/checker-framework/commit/6a7d71c8cbba0c3c14547d4c06ddb500d15c71d2"><code>6a7d71c</code></a> Gradle formatting</li>
<li><a href="https://github.com/typetools/checker-framework/commit/c10d86a0c787c2e5ca95a2c5bb9f4c598b23504e"><code>c10d86a</code></a> Update plugin com-gradleup-shadow to v9.4.3 (<a href="https://redirect.github.com/typetools/checker-framework/issues/7778">#7778</a>)</li>
<li><a href="https://github.com/typetools/checker-framework/commit/ec79d1f81a434153c13e0fb83692119304cf2908"><code>ec79d1f</code></a> Update Gradle to v9.6.1 (<a href="https://redirect.github.com/typetools/checker-framework/issues/7779">#7779</a>)</li>
<li><a href="https://github.com/typetools/checker-framework/commit/f95a2e030e54bae2e26a5e7fa47177acceb4ef6b"><code>f95a2e0</code></a> More examples for <code>-AresourceLeakIgnoredExceptions</code> (<a href="https://redirect.github.com/typetools/checker-framework/issues/7774">#7774</a>)</li>
<li><a href="https://github.com/typetools/checker-framework/commit/79948a2df22a82425a3a17b70b6d784c812d7d5d"><code>79948a2</code></a> Update Gradle to v9.6.0 (<a href="https://redirect.github.com/typetools/checker-framework/issues/7775">#7775</a>)</li>
<li><a href="https://github.com/typetools/checker-framework/commit/e013552e6274b87c9f5dd1c768b4dd12a828707f"><code>e013552</code></a> Update actions/checkout action to v7 (<a href="https://redirect.github.com/typetools/checker-framework/issues/7776">#7776</a>)</li>
<li><a href="https://github.com/typetools/checker-framework/commit/4ba90c265ca8ee0ad4da7ce67af275ee6c7c40e1"><code>4ba90c2</code></a> Update plugin com-diffplug-spotless to v8.7.0 (<a href="https://redirect.github.com/typetools/checker-framework/issues/7773">#7773</a>)</li>
<li>Additional commits viewable in <a href="https://github.com/typetools/checker-framework/compare/checker-framework-4.2.0...checker-framework-4.2.1">compare view</a></li>
</ul>
</details>
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</details>

Fixes #5948

COPYBARA_INTEGRATE_REVIEW=#5948 from google:dependabot/maven/dependencies-fef32f420f de9bb57
PiperOrigin-RevId: 943369386

Author: dependabot[bot]

core/pom.xml

@@ -364,7 +364,7 @@
       <!-- MIT -->
       <groupId>org.checkerframework</groupId>
       <artifactId>checker-qual</artifactId>
-      <version>4.2.0</version>
+      <version>4.2.1</version>
       <scope>test</scope>
     </dependency>
   </dependencies>