mini_magick 4.12.0 on Ruby Gems

Added new tmpdir configuration, which defaults to Dir.tmpdir (#541)

MiniMagick.configure do |config|
  config.tmpdir = File.join(Dir.tmpdir, "/my/new/tmp_dir")
end

Don't leave temporary files lying around when MiniMagick::Image#format failed (#547)
Replace File.exists? with File.exist?, which should fix Ruby 3.2 compatibility (#550)
Fixed a case where the log could not be parsed correctly when there were multiple lines (#540)
Added status to the exception message when the ImageMagick command fails (#542)
Allow passing format to Image#get_pixels so we can request "RGBA" pixels (#537)
Suppress warning to ambiguous argument (#529)
Use Thread#join with a timeout argument instead of the Timeout standard library (#525)