Consider adding `MOTHERDUCK_TOKEN` secret to the Dependabot app

[edgarrmondragon]

Describe the bug

This would allow dependabot PRs like https://github.com/jwills/target-duckdb/pull/39 to pass integration tests.

To Reproduce

NA

Expected behavior

More confidence on merging dependabot PRs.

Screenshots

NA

Your environment

NA

Additional context

• https://docs.github.com/en/code-security/dependabot/working-with-dependabot/configuring-access-to-private-registries-for-dependabot#adding-a-repository-secret-for-dependabot
• https://docs.github.com/en/code-security/dependabot/working-with-dependabot/automating-dependabot-with-github-actions#accessing-secrets