Fix dependabot warning regarding flatten lib

[jscheffl]

Some dependabot warnings for flattenlib are reported, this PR fixes the dependency problem.

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

[eladkal]

might be easier for cherry picking if split providers and core to separate PRs

[jscheffl]

That is right! Let me split!