Update Drupal::VERSION in dev branch

Currently 11.x branch defines core version as 11.0-dev which is not correct.
This makes it hard for modules to adjust their behavior according to the Drupal core version.

For instance, I have to check Drupal version in tests because of some changes in Drupal 11.1. Right now its failing because 11.x is recognized as 11.0.

\version_compare(\Drupal::VERSION, '11.1', '<')

Expected behavior
Drupal::VERSION to be set as 11.1-dev. Once Drupal 11.1 is released it should be updated to 11.2-dev.