Update open-uri test to work on Ruby 3

Author: eregon

.github/workflows/build.yml

@@ -119,7 +119,7 @@ jobs:
     - run: ruby --version
     - run: gem --version
     - run: rake --version
-    - run: ruby -ropen-uri -e 'puts open(%{https://rubygems.org/}) { |f| f.read(1024) }'
+    - run: ruby -ropen-uri -e 'puts URI.send(:open, %{https://rubygems.org/}) { |f| f.read(1024) }'
     - run: gem install json:2.2.0 --no-document
     - run: bundle --version
     - run: bundle install