Replace usages of AssertLegacyTrait::assertResponse(), which is deprecated

Problem/Motivation

AssertLegacyTrait::assertResponse() is deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use $this->assertSession()->statusCodeEquals() instead. See https://www.drupal.org/node/3129738

Proposed resolution

Replace usages of AssertLegacyTrait::assertResponse().

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet