Upgrade `spring` to `2.1.1`

What does this MR do?

The Ruby 2.7 and Bundler 2.1.4 require newer spring, otherwise it fails loading gems:

$ bin/rspec spec/requests/api/debian_project_packages_spec.rb:18
[DEPRECATED] `Bundler.with_clean_env` has been deprecated in favor of `Bundler.with_unbundled_env`. If you instead want the environment before bundler was originally loaded, use `Bundler.with_original_env` (called at /data/cache/bundle-2.7/gems/spring-2.0.2/lib/spring/application_manager.rb:95)
Could not find tzinfo-1.2.8 in any of the sources
Run `bundle install` to install missing gems.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines