[Icon Update] Add variant for CircleCI

[sandy-tpp]

Variant Request

Icon: CircleCI (circleci)
Page: https://thesvg.org/icon/circleci

Which variant is missing?

dark

SVG source

n/a

[thegdsks]

This variant request doesn't include a source SVG (the submission form shows SVG source: n/a), so I can't fabricate a dark-background mark from scratch. CircleCI's official logo assets are on their brand portal (https://brand.circleci.com/613faff00/p/732047-logos), linked from https://circleci.com/legal/trademark-guidelines/. If you can grab the white/dark-background SVG from there and paste its contents (or a link to the raw file) in a comment, I'll add it as the dark variant.