admin: Update FUNDING.yml

[jemgillam]

It's time to remove Patreon from our funding sources.

Description

Performance impact

Security impact

Checklist

• [ ] My code matches the project's code style and yarn lint:fix passes.
• [ ] I've added tests for the new feature, and yarn test passes.
• [ ] I have detailed the new feature in the relevant documentation.
• [ ] I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• [ ] If this is a breaking change I've explained why.