Enable rubocop-thread_safety plugin

Author: horgh

.rubocop.yml

@@ -2,6 +2,7 @@ plugins:
     - rubocop-minitest
     - rubocop-performance
     - rubocop-rake
+    - rubocop-thread_safety
 
 AllCops:
     TargetRubyVersion: '3.2'

maxmind-db.gemspec

@@ -27,4 +27,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rubocop-minitest'
   s.add_development_dependency 'rubocop-performance'
   s.add_development_dependency 'rubocop-rake'
+  s.add_development_dependency 'rubocop-thread_safety'
 end

test/test_reader.rb

@@ -378,7 +378,9 @@ def test_threads
 
     threads = []
     num_threads.times do |i|
+      # rubocop:disable ThreadSafety/NewThread
       threads << Thread.new do
+        # rubocop:enable ThreadSafety/NewThread
         num_lookups.times do |j|
           thread_lookups[i] << reader.get("65.115.240.#{j}")
           thread_lookups[i] << reader.get("2a02:2770:3::#{j}")