Fix serialize type deprecation warning on Rails 7.1+ #11

Job	Run time
Ruby 2.6 / Gemfile gemfiles/rails_5_0.gemfile	29s
Ruby 2.6 / Gemfile gemfiles/rails_5_1.gemfile	33s
Ruby 2.6 / Gemfile gemfiles/rails_5_2.gemfile	24s
Ruby 2.6 / Gemfile gemfiles/rails_6_0.gemfile	29s
Ruby 2.6 / Gemfile gemfiles/rails_6_1.gemfile	30s
Ruby 2.7 / Gemfile gemfiles/rails_5_0.gemfile	33s
Ruby 2.7 / Gemfile gemfiles/rails_5_1.gemfile	38s
Ruby 2.7 / Gemfile gemfiles/rails_5_2.gemfile	25s
Ruby 2.7 / Gemfile gemfiles/rails_6_0.gemfile	27s
Ruby 2.7 / Gemfile gemfiles/rails_6_1.gemfile	34s
Ruby 2.7 / Gemfile gemfiles/rails_7_0.gemfile	28s
Ruby 3.0 / Gemfile gemfiles/rails_6_0.gemfile	9s
Ruby 3.0 / Gemfile gemfiles/rails_6_1.gemfile	10s
Ruby 3.0 / Gemfile gemfiles/rails_7_0.gemfile	10s
Ruby 3.1 / Gemfile gemfiles/rails_6_0.gemfile	11s
Ruby 3.1 / Gemfile gemfiles/rails_6_1.gemfile	12s
Ruby 3.1 / Gemfile gemfiles/rails_7_0.gemfile	12s
	6m 34s

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