Bump pydantic min version to 2.12.3

[gopidesupavan]

CI started failing in the lowest-deps tests: https://github.com/apache/airflow/actions/runs/23058551095/job/66982917534?pr=63531#step:8:2304.

It looks like lowest-deps is resolving pydantic to 2.12.0, which is causing the failures. after testing in local with 2.12.3 its working fine for this version. looking at the changelog https://docs.pydantic.dev/latest/changelog/#v2123-2025-10-17 thats potential fix? didnt deep dive.

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[github-actions]

Backport failed to create: v3-1-test. View the failure log Run details

Note: As of Merging PRs targeted for Airflow 3.X
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.

In matter of doubt please ask in #release-management Slack channel.

Status	Branch	Result
❌	v3-1-test

You can attempt to backport this manually by running:

cherry_picker 9516a77 v3-1-test

This should apply the commit to the v3-1-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue

If you don't have cherry-picker installed, see the installation guide.