MDL-67673 phpunit: Fix the return type of template methods

All the setup/teardown/pre/post/conditions template methods
now are required to return void. This was warned with phpunit 7
and now is enforced.

At the same time, fix a few wrong function names,
provider data and param types, return statements...

backup/controller/tests/controller_test.php

@@ -38,7 +38,7 @@ class core_backup_controller_testcase extends advanced_testcase {
     protected $courseid;  // course id used for testing
     protected $userid;    // user used if for testing
 
-    protected function setUp() {
+    protected function setUp(): void {
         global $DB, $CFG;
 
         $this->resetAfterTest(true);