Remove the vendor directory in .gitignore as these dependencies are needed for php-imap

plugins/php-imap/vendor/phpunit/php-code-coverage/src/Exception/TestIdMissingException.php

@@ -0,0 +1,20 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of phpunit/php-code-coverage.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\CodeCoverage;
+
+use RuntimeException;
+
+final class TestIdMissingException extends RuntimeException implements Exception
+{
+    public function __construct()
+    {
+        parent::__construct('Test ID is missing');
+    }
+}