[ImgBot] Optimize images (#5943)

*Total -- 115.45kb -> 73.67kb (36.19%)

/public/img/gogs-hero.png -- 58.29kb -> 34.18kb (41.37%)
/public/img/favicon.png -- 57.15kb -> 39.48kb (30.91%)

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

Co-authored-by: Imgbot <help@imgbot.net>

[CI SKIP]