Replace the uses of \Drupal::service with dependency injection in ReadinessValidationManager wherever possible

Problem/Motivation

in #3236299: User should not be allowed to do update if it is from minor version to another minor version we found that at some places \Drupal::service is used instead of dependency injection. As dependency injection is the preferred method for accessing and using services in Drupal it should be used wherever possible.

Proposed resolution

Replace the uses of \Drupal::service with dependency injection in ReadinessValidationManager wherever possible.