graphics/darktable: Update to 3.6.0

Release notes:

• https://www.darktable.org/2021/07/darktable-3-6/
• https://github.com/darktable-org/darktable/releases/tag/release-3.6.0

Thank you to Ludger Bolmerg <lbolmerg@posteo.de> for the initial version
of the patch!

PR: 257061