Hover on social media icons isn't consistent

[tim-schilling]

The hover style for social media icons either changes the color to light blue (twitter), doesn't change the color (mastodon) or changes it to white (website). These should all act the same and preferably change the color to either our design's secondary color, or be made to match the twitter icon's style.

This issue is visible on https://2023.djangocon.us/organizers/