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/Core/Cache/MemcacheCacheTest.php

@@ -56,7 +56,7 @@ class MemcacheCacheTest extends MemoryCacheTest
 		return $this->cache;
 	}
 
-	protected function tearDown()
+	protected function tearDown(): void
 	{
 		$this->cache->clear(false);
 		parent::tearDown();