Fixed phpunit configuration warning with phpunit --migrate-configurat…

…ion.

phpunit.xml.dist

@@ -1,23 +1,24 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit backupGlobals="false"
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
+         backupGlobals="false"
          backupStaticAttributes="false"
          colors="true"
          convertErrorsToExceptions="true"
          convertNoticesToExceptions="true"
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         bootstrap="vendor/autoload.php"
->
-    <testsuites>
-        <testsuite name="Detailed result printer for PHPUnit Test Suite">
-            <directory suffix=".phpt">./tests/</directory>
-        </testsuite>
-    </testsuites>
-    <filter>
-        <whitelist>
-            <directory>./src</directory>
-        </whitelist>
-    </filter>
+         bootstrap="vendor/autoload.php">
+  <coverage>
+    <include>
+      <directory>./src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="Detailed result printer for PHPUnit Test Suite">
+      <directory suffix=".phpt">./tests/</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>