fix: Report type missing for cohort results on data downloads

[wgu-jesse-stewart]

Fixes: #38092

Description

This PR fixes a bug where cohort results reports generated from uploading a CSV file to add learners to cohorts would display "Unknown" as the report type in the data downloads table.

What changed:

• Added COHORT_RESULTS to the ReportType enum in lms/djangoapps/instructor/constants.py
• Updated the _detect_report_type_from_filename method in lms/djangoapps/instructor/views/api_v2.py to properly detect cohort results files by matching the 'cohort_results' string in filenames

Impact:

• User roles affected: Course Instructors and Course Staff
• User-facing change: The "Report Type" column in the data downloads table will now correctly display "cohort_results" instead of "Unknown" for cohort assignment reports

Before:

Report Type	Report Name
Unknown	OpenedX_DemoX_DemoCourse_cohort_results_2026-03-04-1725.csv

After:

Report Type	Report Name
Cohort Results	OpenedX_DemoX_DemoCourse_cohort_results_2026-03-04-1725.csv

Supporting information

#38092

Testing instructions

1. Navigate to the Instructor Dashboard for any course
2. Go to the "Membership" tab
3. Under "Cohort Management", upload a CSV file to add learners to a cohort
4. After the upload completes, navigate to the "Data Downloads" tab
5. Verify that the generated cohort results report shows "cohort_results" as the Report Type instead of "Unknown"

Alternative testing via API:

1. Generate a cohort results report using the bulk cohort assignment feature
2. Call the API endpoint: GET /api/instructor/v2/courses/{course_id}/reports
3. Verify that the response includes "report_type": "cohort_results" for cohort result files

Deadline

None

Other information

• This is a minor bug fix with no breaking changes
• No database migrations required
• No configuration changes needed
• No dependencies on other changes

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[dwong2708]

LGTM! Thanks.

[dwong2708]

Sorry, I forgot something, could you update this test to include this change?

[wgu-taylor-payne]

LGTM!