fix(build): Ignore default-source.svg from image optimization

[nickvergessen]

• Resolves: build/image-optimization.sh needs adjusting #40410

Summary

• Added colors for the skipped entries to recognize them easier
• Added the intentional "broken" svg to the ignore list, otherwise theming: Revert broken SVG optimization in default-source.svg #40329 will happen just again

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

I would prefer checking if the svg contains an <image/> tag to avoid this problem in other files as well. Right now this is the only file afaik, but maybe there will be more in the future