Log Message:
print/ruby-rbpdf: update to 1.21.1

1.21.1 (2023-03-20)

* Changed version description of PDF PRODUCER. (#83)
* fix isValidCSSSelectorForTag method. (#82)
* Improved compatibility with ImageMagick 7.1.1-0 and later when using
  mini_magick. (#81)
* Fixed parsepng method to support transparent GIF and PNG tRNS
  transparency. (#80)
* ImageMagick7 support in RMagick 5.2.0. (#79)
* Add support WebP image. (#77)