fix: validate END_DATE is not before START_DATE

[Copilot]

Pull Request

Proposed Changes

The action silently fails with an empty report when END_DATE is set before START_DATE. This adds validation to catch the misconfiguration early with a clear error message.

Implementation

• Added validate_date_range() in env.py: Validates END_DATE ≥ START_DATE using string comparison (YYYY-MM-DD allows lexicographic ordering). Only runs when both dates are provided.
• Integrated into get_env_vars(): Called after format validation, before any processing.
• Added test coverage: Three test cases covering invalid range (raises ValueError), equal dates (allowed), and valid range (allowed).

Error message:

END_DATE ('2024-01-01') must be on or after START_DATE ('2025-01-01')

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing
• If publishing new data to the public (scorecards, security scan results, code quality results, live dashboards, etc.), please request review from @jeffrey-luszcz

Reviewer

• Label as either bug, documentation, enhancement, infrastructure, maintenance or breaking

Original prompt

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This section details on the original issue you should resolve

<issue_title>No check for end date that points to before start date</issue_title>
<issue_description>### Describe the bug

If you set the end date to a time before the start date the action will report success but have an empty report. (silent failure)

To Reproduce

set end date to 2024-01-01
set start date to 2025-01-01
set other required configs
observe an empty report with no indication of what you did wrong

Expected behavior

the action should run a check that the start date is pointing to a time before the end date.

Screenshots

No response

Additional context

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes No check for end date that points to before start date #381

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