Fix tests

- Fix InstallerTest case
- Fix native function mocking
- Add returntype for Unit-Tests
- Fixing ExtendedPDO test troubles
- Fix wrong class inheritance path for DatabaseTestTrait.php
- Fix SyslogLogger Server Exception for PHP8
- Add user/contact to database.fixture.php
- Avoid invalid rollbacks for test setup in PHP8

tests/src/Model/Storage/FilesystemStorageTest.php

@@ -39,7 +39,7 @@ class FilesystemStorageTest extends StorageTest
 	/** @var MockInterface|IConfig */
 	protected $config;
 
-	protected function setUp()
+	protected function setUp(): void
 	{
 		$this->setUpVfsDir();