Move to phpunit9

We require php7.3 now

phpstan.neon

@@ -8,7 +8,7 @@ parameters:
         - src
         - tests
     bootstrapFiles:
-        - bin/.phpunit/phpunit-8-0/vendor/autoload.php
+        - bin/.phpunit/phpunit-9-0/vendor/autoload.php
     excludes_analyse:
         - tests/bootstrap.php
         - src/Swagger/DocumentationNormalizer.php

phpunit.xml.dist

 <?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/6.5/phpunit.xsd"
-         backupGlobals="false"
-         colors="true"
-         bootstrap="tests/bootstrap.php"
->
-    <php>
-        <ini name="error_reporting" value="-1" />
-        <server name="APP_ENV" value="test" force="true" />
-        <server name="KERNEL_CLASS" value="App\Kernel" />
-        <server name="SHELL_VERBOSITY" value="-1" />
-        <server name="SYMFONY_PHPUNIT_REMOVE" value="" />
-        <server name="SYMFONY_PHPUNIT_VERSION" value="8" />
-    </php>
-
-    <testsuites>
-        <testsuite name="Project Test Suite">
-            <directory>tests</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist>
-            <directory>src</directory>
-            <directory>tests</directory>
-        </whitelist>
-    </filter>
-
-    <listeners>
-        <listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener" />
-    </listeners>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" backupGlobals="false" colors="true" bootstrap="tests/bootstrap.php">
+  <coverage>
+    <include>
+      <directory>src</directory>
+      <directory>tests</directory>
+    </include>
+  </coverage>
+  <php>
+    <ini name="error_reporting" value="-1"/>
+    <server name="APP_ENV" value="test" force="true"/>
+    <server name="KERNEL_CLASS" value="App\Kernel"/>
+    <server name="SHELL_VERBOSITY" value="-1"/>
+    <server name="SYMFONY_PHPUNIT_REMOVE" value=""/>
+    <server name="SYMFONY_PHPUNIT_VERSION" value="9"/>
+  </php>
+  <testsuites>
+    <testsuite name="Project Test Suite">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+  <listeners>
+    <listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener"/>
+  </listeners>
 </phpunit>