fix(ui): guard against null/undefined dates in Gantt chart to prevent RangeError

[idrisakorede]

Fix Grid View crash (RangeError: Invalid time value) when viewing tasks in non-terminal states (scheduled, running) with "Show Gantt" enabled. This is a regression from 3.1.7 introduced by #61250.

Root cause: dayjs(value).toISOString() is called on null/undefined date values for tasks that haven't completed yet.

Changes in utils.ts:

• Group/mapped task guard: === null → falsy check (!value) to also catch undefined
• Individual task tries: added !tryInstance.end_date fallback so null end dates use current time instead of crashing

No test coverage or behavior changes beyond the null guard. Tasks with missing end dates now render a bar extending to "now" (consistent with running task behavior).

closes: #63954

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[potiuk]

@idrisakorede This PR has been converted to draft because it does not yet meet our Pull Request quality criteria.

Issues found:

• ❌ Pre-commit / static checks: Failing: CI image checks / Static checks. Run prek run --from-ref main locally to find and fix issues. See Pre-commit / static checks docs.

What to do next:

• The comment informs you what you need to do.
• Fix each issue, then mark the PR as "Ready for review" in the GitHub UI - but only after making sure that all the issues are fixed.
• There is no rush — take your time and work at your own pace. We appreciate your contribution and are happy to wait for updates.
• Maintainers will then proceed with a normal review.

Converting a PR to draft is not a rejection — it is an invitation to bring the PR up to the project's standards so that maintainer review time is spent productively. There is no rush — take your time and work at your own pace. We appreciate your contribution and are happy to wait for updates. If you have questions, feel free to ask on the Airflow Slack.

[pierrejeambrun]

Flaky e2e test, merging.

[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 92255b5 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.

[pierrejeambrun]

manual backport for 3.2.0 #64489