Merge pull request #146 from rails/flavorjones-ci-fix-ubuntu-system-library-test

ci: pin system lib test to 20.04

Author: flavorjones

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       - run: bundle exec rake
 
   cruby-nokogiri-system-libraries:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - uses: ruby/setup-ruby@v1