Bump args from 2.5.0 to 2.6.0 in /test_utilities (#3974)

Bumps [args](https://github.com/dart-lang/core) from 2.5.0 to 2.6.0.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/dart-lang/core/releases">args's releases</a>.</em></p>
<blockquote>
<h2>package:args v2.6.0</h2>
<ul>
<li>Added source argument when throwing a <code>ArgParserException</code>.</li>
<li>Fix inconsistent <code>FormatException</code> messages</li>
<li>Require Dart 3.3</li>
<li>Move to <code>dart-lang/core</code> monorepo.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/dart-lang/core/commit/8c5dca81f8ad1c3f2363cd800f80f51b5a7d940e"><code>8c5dca8</code></a> Merge pull request <a href="https://redirect.github.com/dart-lang/core/issues/2">#2</a> from dart-lang/merge-args-package</li>
<li><a href="https://github.com/dart-lang/core/commit/6ea8a85b3cb0f5f7131f79e6805c08304ef95d20"><code>6ea8a85</code></a> Add label workflow</li>
<li><a href="https://github.com/dart-lang/core/commit/7137af2fe208d3e08b7c4b8b5f845ad8dae468c3"><code>7137af2</code></a> Add readme</li>
<li><a href="https://github.com/dart-lang/core/commit/e6b4d3adee59d09ce5b4f3c736559229d7b3954f"><code>e6b4d3a</code></a> Fix tags regex</li>
<li><a href="https://github.com/dart-lang/core/commit/00d89bc651b5c53f6f039523e543f736f654a55d"><code>00d89bc</code></a> Rev pubspec version</li>
<li><a href="https://github.com/dart-lang/core/commit/4896f8abe2ed959d9a3b9892e850bdd97332ffbe"><code>4896f8a</code></a> Fix workflows again</li>
<li><a href="https://github.com/dart-lang/core/commit/5560a0567fe07e0d96fd45a00b80e635064d6027"><code>5560a05</code></a> Fix workflows</li>
<li><a href="https://github.com/dart-lang/core/commit/2d6cddf6dc4906d2817df8f942800deac18097b1"><code>2d6cddf</code></a> Merge package:args into shared core repository</li>
<li><a href="https://github.com/dart-lang/core/commit/315f7f9505c5699c40a0ece91a028eddec87437b"><code>315f7f9</code></a> Bump actions/checkout from 4.1.7 to 4.2.0 in the github-actions group (dart-l...</li>
<li><a href="https://github.com/dart-lang/core/commit/272f17532c93b40719373dd0c63b4d02c6294e48"><code>272f175</code></a> Add argument name when throwing a <code>ArgParserException</code><code>dart-archive/args#283</code></li>
<li>Additional commits viewable in <a href="https://github.com/dart-lang/core/compare/args-v2.5.0...args-v2.6.0">compare view</a></li>
</ul>
</details>
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test_utilities/pubspec.yaml

@@ -10,6 +10,6 @@ environment:
   sdk: '>=2.18.0 < 4.0.0'
 
 dev_dependencies:
-  args: 2.5.0
+  args: 2.6.0
   yaml: 3.1.2
   path: 1.9.0