EntityListBuilder should return URL object vs mock

Problem/Motivation

Discovered in #2852898: 508 Compliance Issue -Edit links on content page are not unique the mock of URL didn’t return a URL object. So when we went to get options it failed.

Steps to reproduce

Apply the MR from #2852898: 508 Compliance Issue -Edit links on content page are not unique
Run Drupal\Tests\Core\Entity\EntityListBuilder

Proposed resolution

Fix the test that is failing

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet