Fix failures on ruby 3.1

Because https://github.com/ruby/ruby/pull/5148 merged after Ruby 3.1.0 released.

https://github.com/ruby/actions/runs/4705986643?check_suite_focus=true#step:18:144
```
  1)
  Method#parameters adds * rest arg for "star" argument FAILED
  Expected [[:rest]] == [[:rest, :*]]
  to be truthy but was false
  /home/runner/work/actions/actions/snapshot-ruby_3_1/spec/ruby/core/method/parameters_spec.rb:228:in `block (3 levels) in <top (required)>'
  /home/runner/work/actions/actions/snapshot-ruby_3_1/spec/ruby/core/method/parameters_spec.rb:4:in `<top (required)>'

  2)
  Proc#parameters adds * rest arg for "star" argument FAILED
  Expected [[:req, :x], [:rest]] == [[:req, :x], [:rest, :*]]
  to be truthy but was false
  /home/runner/work/actions/actions/snapshot-ruby_3_1/spec/ruby/core/proc/parameters_spec.rb:85:in `block (3 levels) in <top (required)>'
  /home/runner/work/actions/actions/snapshot-ruby_3_1/spec/ruby/core/proc/parameters_spec.rb:3:in `<top (required)>'
```

spec/ruby/core/method/parameters_spec.rb

@@ -222,14 +222,14 @@ describe "Method#parameters" do
     m.method(:handled_via_method_missing).parameters.should == [[:rest]]
   end
 
-  ruby_version_is '3.1' do
+  ruby_version_is '3.2' do
     it "adds * rest arg for \"star\" argument" do
       m = MethodSpecs::Methods.new
       m.method(:one_unnamed_splat).parameters.should == [[:rest, :*]]
     end
   end
 
-  ruby_version_is ''...'3.1' do
+  ruby_version_is ''...'3.2' do
     it "adds nameless rest arg for \"star\" argument" do
       m = MethodSpecs::Methods.new
       m.method(:one_unnamed_splat).parameters.should == [[:rest]]