Fixes BBC Blocks Dark Mode Base64 String Size

[HarveyPeachey]

Part of https://github.com/bbc/simorgh/issues/10004

Overall change: This PR fixes the base 64 string for the dark mode BBC blocks image which is used in placeholders, this takes the normal BBC Blocks logo, replaces the fill colour in the SVG format, and has been converted back into the base 64 format.

Makes the image 3x smaller, from 8.27 KB to 2.70 KB.

Code changes:

• Replaces BBC blocks dark mode logo with smaller string size base 64 logo
• Updates snapshot
• Bumps dependant packages, and updates changelogs

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• [x] (BBC contributors only) This PR follows the repository use guidelines
• [x] I have assigned myself to this PR and the corresponding issues
• [x] Automated jest tests added (for new features) or updated (for existing features)
• [ ] This PR requires manual testing