Bump phpstan/phpstan-phpunit from 1.3.14 to 1.3.15 (#1807)

Bumps
[phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit)
from 1.3.14 to 1.3.15.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/phpstan/phpstan-phpunit/releases">phpstan/phpstan-phpunit's
releases</a>.</em></p>
<blockquote>
<h2>1.3.15</h2>
<ul>
<li><a
href="http://github.com/phpstan/phpstan-phpunit/commit/70ecacc64fe8090d8d2a33db5a51fe8e88acd93a">70ecacc</a>
- AssertTypeSpecifyingExtensionHelper: rootExpr with unknown variable to
avoid always-true false positives (<a
href="https://redirect.github.com/phpstan/phpstan-phpunit/issues/197">#197</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/phpstan/phpstan-phpunit/commit/70ecacc64fe8090d8d2a33db5a51fe8e88acd93a"><code>70ecacc</code></a>
AssertTypeSpecifyingExtensionHelper: rootExpr with unknown variable to
avoid ...</li>
<li>See full diff in <a
href="https://github.com/phpstan/phpstan-phpunit/compare/1.3.14...1.3.15">compare
view</a></li>
</ul>
</details>
<br />


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composer.json

@@ -52,7 +52,7 @@
     "phpstan/phpstan": "1.10.36",
     "phpstan/phpstan-deprecation-rules": "1.1.4",
     "phpstan/phpstan-mockery": "1.1.1",
-    "phpstan/phpstan-phpunit": "1.3.14",
+    "phpstan/phpstan-phpunit": "1.3.15",
     "phpstan/phpstan-strict-rules": "1.5.1",
     "phpunit/phpunit": "9.6.4",
     "friendsofphp/php-cs-fixer": "3.17.0"