MDL-81919 core: Correct mapped class location

Author: andrewnicols

lib/db/legacyclasses.php

@@ -30,7 +30,7 @@
 // The old class name is the key, the path to the file containing the class is the vlaue.
 // The array must be called $legacyclasses.
 $legacyclasses = [
-    \bootstrap_renderer::class => 'output\bootstrap_renderer',
+    \bootstrap_renderer::class => 'output/bootstrap_renderer.php',
     \coding_exception::class => 'exception/coding_exception.php',
     \file_serving_exception::class => 'exception/file_serving_exception.php',
     \invalid_dataroot_permissions::class => 'exception/invalid_dataroot_permissions.php',