fix: migrate phpunit configuration

phpunit.xml.dist

@@ -1,32 +1,28 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
 <!-- https://phpunit.de/manual/current/en/appendixes.configuration.html -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/6.1/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
          backupGlobals="false"
          colors="true"
          bootstrap="vendor/autoload.php"
 >
-    <php>
-        <!-- define your env variables for the test env here -->
-    </php>
-
-    <listeners>
-        <listener class="M6WebTest\Tornado\Adapter\Amp\LoopReset" />
-    </listeners>
-
-    <testsuites>
-        <testsuite name="Tornado Test Suite">
-            <directory>tests</directory>
-        </testsuite>
-        <testsuite name="Tornado Examples">
-            <directory>examples/tests</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist>
-            <directory>src</directory>
-        </whitelist>
-    </filter>
+  <coverage>
+    <include>
+      <directory>src</directory>
+    </include>
+  </coverage>
+  <php>
+    <!-- define your env variables for the test env here -->
+  </php>
+  <listeners>
+    <listener class="M6WebTest\Tornado\Adapter\Amp\LoopReset"/>
+  </listeners>
+  <testsuites>
+    <testsuite name="Tornado Test Suite">
+      <directory>tests</directory>
+    </testsuite>
+    <testsuite name="Tornado Examples">
+      <directory>examples/tests</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>