Rename \Drupal\router_test\TestControllers and its methods

Problem/Motivation

In 📌 Add void return typehints to all test methods Active we almost accidentally committed some out of scope changes to core/modules/system/tests/modules/router_test_directory/src/TestControllers.php because it matched the path glob patterns used for rector. It's inside a tests directory, and it has function names starting with test. The function names also give no indication as to what they do, just named test1, test2 and so on.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet