graphics/ruby-mini-magick: update to 4.12.0

4.12.0 (2022-12-06)

* 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)

(taca)