Tests fails on Ruby 3.1.0

Problem

As the title says, some tests fail on Ruby 3.1.0.

https://github.com/x-motemen/git-pr-release/runs/4501404152?check_suite_focus=true

  1) Git::Pr::Release::CLI#fetch_merged_prs is expected to receive git("merge-base", "42bd43b80c973c8f348df3521745201be05bf194", "origin/master") 1 time
     Failure/Error: @pr_3 = Sawyer::Resource.new(agent, YAML.load_file(file_fixture("pr_3.yml")))

     Psych::DisallowedClass:
       Tried to load unspecified class: Time
     # ./spec/git/pr/release/cli_spec.rb:222:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:25:in `block (2 levels) in <top (required)>'
     # ./vendor/bundle/ruby/3.1.0/gems/webmock-3.14.0/lib/webmock/rspec.rb:37:in `block (2 levels) in <top (required)>'

x-motemen / git-pr-release

Tests fails on Ruby 3.1.0 #72

Problem