Fixed RBAC databases tests

tests were reusing static DB connection instance resulting in all tests
to be run against MySQL only!

PgSQL and Sqlite tests are now failing because of the issue reported in #13501.

tests/framework/rbac/PgSQLManagerCacheTest.php

@@ -0,0 +1,29 @@
+<?php
+namespace yiiunit\framework\rbac;
+
+use yii\caching\FileCache;
+use yii\rbac\DbManager;
+
+/**
+ * PgSQLManagerTest
+ * @group db
+ * @group rbac
+ * @group pgsql
+ */
+class PgSQLManagerCacheTest extends DbManagerTestCase
+{
+    protected static $driverName = 'pgsql';
+
+    /**
+     * @return \yii\rbac\ManagerInterface
+     */
+    protected function createManager()
+    {
+        return new DbManager([
+            'db' => $this->getConnection(),
+            'cache' => new FileCache(['cachePath' => '@yiiunit/runtime/cache']),
+            'defaultRoles' => ['myDefaultRole']
+        ]);
+    }
+
+}