Banners: adjust nominal SVG size

- by scaling up the nominal size, SVG icons are no longer rendered fuzzy in the banners

Fixes #616
2 jobs for <span class="ref-name">wip/jimmac/fuzzy-svgs</span> in 15 minutes and 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #244351
build-gnome-software

00:15:25

failed #244259
build-gnome-software

00:31:39