Failing tests due to Cairo 1.17.8 subpixel antialiasing update

[MrDiver]

In Cairo Version 1.17.8 there was new subpixel antialiasing introduced based on the changes in 1.17.4. This breaks the behavior of manim because it changes the output of the tests so many tests will fail due to different pixels at the border of mobjects.

One solution might be to increase the error ratio or update the test data. This will most likely break the tests for people using the older cairo version.

[naveen521kk]

FYI, there's a new stable release of Cairo out now https://cairographics.org/news/cairo-1.18.0/

also see #3399 (comment)