api_v3_ExtensionTest::testExtensionGet - Be a little less flaky

The test has a magic number which seems to be based on the number of
extensions in the `drupal-clean` build profile -- which is basically the
smallest number anyone might have.  However, it gives false-negatives if you
have any other extensions around.  Make it a little less flaky.

tests/phpunit/api/v3/ExtensionTest.php

@@ -89,7 +89,7 @@ public function testExtensionGet() {
     $result = $this->callAPISuccess('extension', 'get', array());
     $testExtensionResult = $this->callAPISuccess('extension', 'get', array('key' => 'test.extension.manager.paymenttest'));
     $this->assertNotNull($result['values'][$testExtensionResult['id']]['typeInfo']);
-    $this->assertEquals(6, $result['count']);
+    $this->assertTrue($result['count'] >= 6);
   }
 
   public function testGetMultipleExtensions() {