Add explicit inverse_of option to associations

app/models/experiment.rb

@@ -2,7 +2,7 @@
 
 class Experiment < ApplicationRecord
   has_many :experiment_users
-  has_many :experiment_subjects
+  has_many :experiment_subjects, inverse_of: :experiment
 
   validates :name, presence: true, uniqueness: true, length: { maximum: 255 }
 

app/models/experiment_subject.rb

@@ -3,7 +3,7 @@
 class ExperimentSubject < ApplicationRecord
   include ::Gitlab::Experimentation::GroupTypes
 
-  belongs_to :experiment
+  belongs_to :experiment, inverse_of: :experiment_subjects
   belongs_to :user
   belongs_to :group
   belongs_to :project