community/ruby-rmagick: upgrade to 4.2.6

https://github.com/rmagick/rmagick/compare/RMagick_4-2-5...RMagick_4-2-6

- Guard against an empty rpath (#1333)
- Remove test_files to reduce gem package size (#1338)
- Added codespaces configurations (#1341)
- Update ImageMagick to 6.9.12-56 and 7.1.0-41 (#1323)
- Call GetImageDistortion instead of IsImagesEqual to fix

builds with imagemagick 7 instead of 6

one test failing, but it's been failing before, so i guess it's fine