同姓同名の Author を登録できるように修正。

app/models/author.rb

@@ -5,7 +5,7 @@ def self.ransackable_attributes(_auth_object = nil)
     %w[name id created_at updated_at]
   end
 
-  validates :name, presence: true, uniqueness: true
+  validates :name, presence: true
 
   has_many :book_author_relationship
   has_many :book_masters, through: :book_author_relationship