[rubygems/rubygems] Skip this spec on ruby_core workflow

ruby_core has an 'ast.rb' file that gets in the
middle and breaks this spec, so it's better we skip
this test on this workflow for now.

Also, slightly change the spec name from "run" to
"runs" and change the last assertion, it's cleaner
to check empty error.
Thanks to David Rodríguez for this!

Signed-off-by: Utkarsh Gupta <utkarsh@debian.org>

https://github.com/rubygems/rubygems/commit/ba8eaa70c3

spec/bundler/commands/newgem_spec.rb

@@ -175,14 +175,15 @@ RSpec.describe "bundle gem" do
       expect(bundled_app("#{gem_name}/.rubocop.yml")).to exist
     end
 
-    it "run rubocop inside the generated gem with no offenses" do
+    it "runs rubocop inside the generated gem with no offenses" do
+      skip "ruby_core has an 'ast.rb' file that gets in the middle and breaks this spec" if ruby_core?
       prepare_gemspec(bundled_app(gem_name, "#{gem_name}.gemspec"))
       rubocop_version = RUBY_VERSION > "2.4" ? "0.85.1" : "0.80.1"
       gems = ["rake", "rubocop -v #{rubocop_version}"]
       path = Bundler.feature_flag.default_install_uses_path? ? local_gem_path(:base => bundled_app(gem_name)) : system_gem_path
       realworld_system_gems gems, :path => path
       bundle "exec rubocop --config .rubocop.yml", :dir => bundled_app(gem_name)
-      expect($?.exitstatus).to eq(0) if exitstatus
+      expect(err).to be_empty
     end
   end