Use ruby 2.7 when pushing cookbooks.

templates/chef.yml

@@ -44,6 +44,7 @@ variables:
   RUBYOPT: "-W0" # Disable ruby warnings.
   EXTRA_PRODUCTS_FILE: cinc-products.rb
   COOKBOOK_PUBLISHER_BRANCH: mattmi/debug-cookbook-upload-failures
+  PUBLISHER_SKIP_VERSION_CHECK: "true"
 before_script:
   - eval $(ssh-agent -s)
@@ -114,6 +115,7 @@ kitchen:
 push-cookbook:
   stage: $[[ inputs.publish_stage ]]
+  image: ruby 2.7
   only:
     refs:
       - master