print/miktex: Update to 21.8.
Changes:
https://github.com/MiKTeX/miktex/releases/tag/21.3 https://github.com/MiKTeX/miktex/releases/tag/21.6.28 https://github.com/MiKTeX/miktex/releases/tag/21.7 https://github.com/MiKTeX/miktex/releases/tag/21.8
PR: 259139
Approved by: arrowd (maintainer)