Follow-up for #2443457: improve \Drupal\block\Tests\Views\DisplayBlockTest::testBlockEmptyRendering()

Problem/Motivation

This will help #2429617: Make D8 2x as fast: Dynamic Page Cache: context-dependent page caching (for *all* users!).

#2443457: Views block displayed when no results returned introduced test coverage, which unfortunately just chose the default frontpage (which is the user login form in the testing install profile) as the route for its testing. But, that route/controller has certain cacheability metadata associated with it that makes it less clear what is being tested.

Proposed resolution

Make what is being tested more clear by using a route that has only the most basic cacheability metadata (because it has a hardcoded render array).

Remaining tasks

Review.

User interface changes

None.

API changes

None.

Data model changes

None.