build(deps): bump boto3 from 1.38.46 to 1.39.3 in /clients/python (kubeflow#1278)

Bumps [boto3](https://github.com/boto/boto3) from 1.38.46 to 1.39.3.
- [Release notes](https://github.com/boto/boto3/releases)
- [Commits](boto/boto3@1.38.46...1.39.3)

---
updated-dependencies:
- dependency-name: boto3
  dependency-version: 1.39.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]