Fix GraphQL/FieldDefinitions offense (Part 4/4)

What does this MR do and why?

This fixes the GraphQL/FieldDefinitions offense in:

• ee/app/graphql/types/ci/code_quality_degradation_type.rb
• ee/app/graphql/types/epic_type.rb
• ee/app/graphql/types/group_release_stats_type.rb
• ee/app/graphql/types/iteration_type.rb
• ee/app/graphql/types/requirements_management/requirement_type.rb

This MR is part 4 of a 4 part series of MRs to resolve #346029.

💁 This is the only MR in this series to modify files from ee/.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #346029