Bump version to 3.4.0 to include reviewer roulette update

Diff

v3.3.0...5f15d3eb

🤔 I'll tweak the release notes manually. Changing how we use the seed shouldn't have external impact, so it probably doesn't need to be mentioned. I also forgot to include changelog for adding the feature to look at the approval rules. I need to better get this into habits.

Checklist

• Diff link is up-to-date.
• Check the release notes: https://gitlab.com/api/v4/projects/gitlab-org%2Fruby%2Fgems%2Fgitlab-dangerfiles/repository/changelog?version=3.4.0
• Based on the diff and the release notes, version.rb is updated, according to SemVer.