Don't drop privs to ubuntu before running Renovate

[negz]

Description of your changes

It seems like earthly bootstrap can talk to docker, but earthly +go-generate can't. My best guess is this is because we bootstrap as root, then try to run earthly as ubuntu.

I have:

• [x] Read and followed Crossplane's contribution process.
• [ ] ~Run earthly +reviewable to ensure this PR is ready for review.~
• [ ] ~Added or updated unit tests.~
• [ ] ~Linked a PR or a docs tracking issue to document this change.~
• [ ] ~Added backport release-x.y labels to auto-backport this PR.~

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