Fix incorrect plugin version

[koic]

require_relative 'rubocop/factory_bot/version' was missing, causing the constant lookup for Version::STRING in lib/rubocop/factory_bot/plugin.rb to resolve to RuboCop::Version::STRING instead of RuboCop::FactoryBot::Version::STRING.

This PR fixes an issue where rubocop -V incorrectly displayed the RuboCop version instead of the rubocop-factory_bot version:

$ bundle exec rubocop -V
1.73.2 (using Parser 3.3.7.1, rubocop-ast 1.38.1, analyzing as Ruby 2.7, running on ruby 3.4.2) [x86_64-darwin23]
  - rubocop-performance 1.24.0
  - rubocop-rake 0.7.1
  - rubocop-capybara 1.73.2
  - rubocop-factory_bot 1.73.2
  - rubocop-rspec_rails 2.31.0
  - rubocop-rspec 3.5.0

Replace this text with a summary of the changes in your PR. The more detailed you are, the better.

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded: "<<next>>" in default/config.yml.

If you have modified an existing cop's configuration options:

• Set VersionChanged: "<<next>>" in config/default.yml.