graphics/krita: update to 4.4.8

This is strictly a bug fix release. The most important reason for this
release is a fix for a performance regression in Krita 4.4.5. There are
a few other fixes:

• Fix a crash on exit with certain versions of Qt and PyQt
• Fix moving selection with the magnetic selection tool (BUG:433633)
• Fix crashes in the magnetic selection tool when deleting nodes (BUG:439896)
• Fix an assert when converting the image color space from Python (BUG:437980)
• Fix a crash when closing a gamut mask document (BUG:438914)
• Fix drag and drop of clone layers between images (BUG:414699)
• Fix crash when saving the image with trimming enabled (BUG:437626)

Note: due to an upstream oversight, the so-version went from 21 back to