MDL-76870 question: change assertion to assertEqualsCanonicalizing

By using that assertion the arrays will be sorted before comparison
preventing any Oracle sorting related failures.

Credits for the solution go to Tim Hunt!

question/tests/backup_test.php

@@ -88,7 +88,8 @@ class core_question_backup_testcase extends advanced_testcase {
             $this->assertTrue($precheck);
         } else {
             $precheckresults = $rc->get_precheck_results();
-            $this->assertEquals(['warnings' => $expectedprecheckwarning], $precheckresults);
+            $this->assertEqualsCanonicalizing($expectedprecheckwarning, $precheckresults['warnings']);
+            $this->assertCount(1, $precheckresults);
         }
         $rc->execute_plan();
         $rc->destroy();