Ignore example groups defined inside examples

Found a lot of this in rspec-core and rspec-mocks

Author: pirj

lib/rubocop/cop/rspec/empty_example_group.rb

@@ -161,6 +161,7 @@ class EmptyExampleGroup < Base
 
         def on_block(node)
           return if node.each_ancestor(:def, :defs).any?
+          return if node.each_ancestor(:block).any? { |block| example?(block) }
 
           example_group_body(node) do |body|
             add_offense(node.send_node) unless examples?(body)

spec/rubocop/cop/rspec/empty_example_group_spec.rb

@@ -282,4 +282,15 @@ def without_yaml_loaded(&block)
       end
     RUBY
   end
+
+  it 'ignores example groups inside examples' do
+    expect_no_offenses(<<~RUBY)
+      RSpec.describe 'rspec-core' do
+        it 'runs an example group' do
+          group = RSpec.describe { }
+          group.run
+        end
+      end
+    RUBY
+  end
 end