Merge pull request #455 from rspec/update-ci-build-scripts-2020-12-21-for-4-0-dev

Updates from rspec-dev (2020-12-21)

Author: JonRowe

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         ruby:
-          - 3.0.0-preview2
+          - 3.0.0-rc1
           - 2.7
           - 2.6
           - 2.5

spec/rspec/support/spec/stderr_splitter_spec.rb

@@ -85,7 +85,7 @@
 
   unless defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx'
     it 'will fail an example which generates a warning' do
-      true unless @undefined
+      true unless $undefined
       expect { splitter.verify_no_warnings! }.to raise_error(/Warnings were generated:/)
     end
   end