MDL-50887 tests: Increment number of plugins in core_component_testcase.

We have got one more core plugin now.

lib/tests/component_test.php

@@ -34,7 +34,7 @@ class core_component_testcase extends advanced_testcase {
     // To be changed if number of subsystems increases/decreases,
     // this is defined here to annoy devs that try to add more without any thinking,
     // always verify that it does not collide with any existing add-on modules and subplugins!!!
-    const SUBSYSTEMCOUNT = 63;
+    const SUBSYSTEMCOUNT = 64;
 
     public function test_get_core_subsystems() {
         global $CFG;