tests: Make loadFixtures public

Some tests will need to load their own database fixtures. By making this
API public we make it easy for them to do so.

This change is needed by the tests for the Superblock addon.

Project......: Improve Superblock Addon
Sponsored-by.: NLnet NGI0 Commons Fund

tests/unit/UnitTestCase.php

@@ -181,7 +181,7 @@ class UnitTestCase extends TestCase {
 	 *						directory of the process, which should normally
 	 *						be the Hubzilla root directory.
 	 */
-	private function loadFixture($file) : void {
+	public function loadFixture($file) : void {
 		$table_name = basename($file, '.yml');
 		$data = yaml_parse_file($file)[$table_name];