Ensure parent manager is injected under v3

- Modified the condition for pulling the parent locator to test against
  the v3 `configure` method instead; `getServiceLocator()` also exists
  in v3, but emits a deprecation notice.
- Modified the test for the behavior to work under both versions. The
  expected behavior is the same, given the same configuration.

Author: weierophinney

src/Helper/Navigation/PluginManager.php

@@ -86,7 +86,7 @@ public function __construct($configOrContainerInstance = null, array $v3config =
             // set the service locator to the parent locator.
             //
             // Under v3, the parent locator is what is passed to the method already.
-            if (method_exists($container, 'getServiceLocator') && $container->getServiceLocator()) {
+            if (! method_exists($container, 'configure') && $container->getServiceLocator()) {
                 $container = $container->getServiceLocator();
             }
 

test/Helper/Navigation/PluginManagerCompatibilityTest.php

@@ -67,13 +67,8 @@ public function testConstructorAllowsConfigInstanceAsFirstArgumentUnderV2()
         $this->assertInstanceOf(PluginManager::class, $helpers);
     }
 
-    public function testInjectsParentContainerIntoHelpersUnderV2()
+    public function testInjectsParentContainerIntoHelpers()
     {
-        $helpers = $this->getPluginManager();
-        if (method_exists($helpers, 'configure')) {
-            $this->markTestSkipped('This test is specific to v2 functionality');
-        }
-
         $config = new Config([
             'navigation' => [
                 'default' => [],