Fix wrong $this->assert...() with `self::assert...()

tests/src/Core/Config/PreloadConfigTest.php

@@ -59,7 +59,7 @@ class PreloadConfigTest extends ConfigTest
 
 		// Assert that every category is loaded everytime
 		foreach ($data as $cat => $values) {
-			$this->assertConfig($cat, $values);
+			self::assertConfig($cat, $values);
 		}
 	}
 
@@ -80,7 +80,7 @@ class PreloadConfigTest extends ConfigTest
 
 		// Assert that every category is loaded everytime and is NOT overwritten
 		foreach ($data1 as $cat => $values) {
-			$this->assertConfig($cat, $values);
+			self::assertConfig($cat, $values);
 		}
 	}