Short answer :
Dir['/path/*.rb'].each { |file| require file }
Explanation :
Dir[] is an equivalent of calling Dir.glob() which take a pattern string and returns an array containing the matching filenames. (cf. more detail about patterns https://ruby-doc.org/core-3.1.1/Dir.html#glob-method)
Exemple with a given directory myDirectory at filesystem root containing only file1.rb and file2.rb, Dir['/myDirectory/*.rb'] will return :
[
  '/myDirectory/file1.rb',
  '/myDirectory/file2.rb'
]
Knowing how Dir.glob works, we just need to iterate on the list of files by passing their names in the require method :
Dir['/myDirectory/*.rb'].each { |file_name| require file_name }