[ImgBot] Optimize images

*Total -- 47.20kb -> 28.03kb (40.61%)

/test/pangocairo.png -- 2.33kb -> 1.00kb (57.06%)
/test/sudoku.png -- 9.58kb -> 4.62kb (51.76%)
/test/glyph_collision.png -- 2.92kb -> 1.44kb (50.75%)
/test/glyph_simple.png -- 4.19kb -> 2.20kb (47.54%)
/test/mi_with_bounds.png -- 2.81kb -> 1.56kb (44.54%)
/test/circle_comparison.png -- 11.80kb -> 6.70kb (43.25%)
/test/comprehensive_test.png -- 13.58kb -> 10.53kb (22.52%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp