fix(tests): Fix PHPUnit 10 support

Author: MasterRO94

.phpunit.cache/test-results

@@ -0,0 +1 @@
+{"version":1,"defects":[],"times":{"MasterRO\\MailViewer\\Tests\\MailLoggerTest::test_it_logs_mailable_recipients":0.097,"MasterRO\\MailViewer\\Tests\\MailLoggerTest::test_it_logs_attachments":0.018,"MasterRO\\MailViewer\\Tests\\MailViewerTest::test_it_receives_mail_logs":0.081,"MasterRO\\MailViewer\\Tests\\MailViewerTest::test_it_receives_mail_log_attachments":0.014,"MasterRO\\MailViewer\\Tests\\MailViewerTest::test_it_receives_mail_log_payload":0.01,"MasterRO\\MailViewer\\Tests\\MailViewerTest::test_it_receives_mail_logs_stats":0.045}}

phpunit.xml

@@ -1,19 +1,19 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit backupGlobals="false"
-         backupStaticAttributes="false"
-         bootstrap="vendor/autoload.php"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         processIsolation="false"
-         stopOnError="false"
-         stopOnFailure="false"
-         verbose="true"
+<phpunit
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  backupGlobals="false"
+  bootstrap="vendor/autoload.php"
+  colors="true"
+  processIsolation="false"
+  stopOnError="false"
+  stopOnFailure="false"
+  xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.0/phpunit.xsd"
+  cacheDirectory=".phpunit.cache"
+  backupStaticProperties="false"
 >
-    <testsuites>
-        <testsuite name="Package Test Suite">
-            <directory suffix="Test.php">./tests/</directory>
-        </testsuite>
-    </testsuites>
+  <testsuites>
+    <testsuite name="Package Test Suite">
+      <directory suffix="Test.php">./tests/</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>