Performance: Check `svgo` in CI

Created by: umpox

Follow on from https://github.com/sourcegraph/sourcegraph/pull/26285

We check for any potential optimizations and fail if found

My initial worry was that svgo wasn't idempotent, as it has a multipass option which goes over an SVG multiple times to make sure it is fully optimized. I tested this by running the command in a loop for like 20 mins and logging any failures - there wasn't any so this should be OK