chore: weaviate - lower-bound pin for python-dateutil

[anakin87]

Related Issues

• failing unit tests with lowest direct dependencies: https://github.com/deepset-ai/haystack-core-integrations/actions/runs/25295161615/job/74237013270 (I am not sure why this did not fail before)

Proposed Changes:

• set a lower-bound pin for python-dateutil (to the first version that introduced parser.isoparse)

How did you test it?

CI

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[github-actions]

Coverage report (weaviate)

This PR does not seem to contain any modification to coverable code.

[sjrl]

Thanks!