Upgrade RuboCop and fix new issues

Let's run RuboCop on Ruby 3.3 on the CI. For that to work, update
RuboCop and fix some new issues from the upgraded version.

Gemfile.lock

@@ -2,33 +2,34 @@ GEM
   remote: https://rubygems.org/
   specs:
     ast (2.4.2)
-    json (2.6.2)
-    parallel (1.22.1)
-    parser (3.1.2.1)
+    json (2.7.2)
+    language_server-protocol (3.17.0.3)
+    parallel (1.26.3)
+    parser (3.3.5.0)
       ast (~> 2.4.1)
+      racc
+    racc (1.8.1)
     rainbow (3.1.1)
-    regexp_parser (2.6.0)
-    rexml (3.3.6)
-      strscan
-    rubocop (1.39.0)
+    regexp_parser (2.9.2)
+    rubocop (1.66.1)
       json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
-      parser (>= 3.1.2.1)
+      parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
-      regexp_parser (>= 1.8, < 3.0)
-      rexml (>= 3.2.5, < 4.0)
-      rubocop-ast (>= 1.23.0, < 2.0)
+      regexp_parser (>= 2.4, < 3.0)
+      rubocop-ast (>= 1.32.2, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.23.0)
-      parser (>= 3.1.1.0)
-    ruby-progressbar (1.11.0)
-    strscan (3.1.0)
-    unicode-display_width (2.3.0)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.32.3)
+      parser (>= 3.3.1.0)
+    ruby-progressbar (1.13.0)
+    unicode-display_width (2.6.0)
 
 PLATFORMS
   aarch64-linux
   arm64-darwin-21
+  arm64-darwin-23
   x86_64-darwin-19
   x86_64-darwin-20
   x86_64-linux

test/helpers/integration_helper.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "./config_helper"
+require_relative "config_helper"
 
 module IntegrationHelper
   def self.wait_for_start

test/helpers/span.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "./config_helper"
+require_relative "config_helper"
 
 class Span
   class << self
@@ -50,7 +50,7 @@ def root
     end
 
     def root!
-      raise "There is no root span" if roots.length.zero?
+      raise "There is no root span" if roots.empty?
       raise "There is more than one root span" if roots.length > 1
 
       root