[SNOW-1478924]: Ensure __getitem__ on DataFrameGroupBy returns SeriesGroupBy when appropriate even if as_index=False

[sfc-gh-rdurrani]

1. Which Jira issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-1478924

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
     • If this test skips Local Testing mode, I'm requesting review from @snowflakedb/local-testing
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency
   • If this is a new feature/behavior, I'm adding the Local Testing parity changes.
   • I acknowledge that I have ensured my changes to be thread-safe. Follow the link for more information: Thread-safe Developer Guidelines

3. Please describe how your code solves the related issue.

Ensure that getitem on a DataFrameGroupBy returns a SeriesGroupBy if only one column is indexed, even if as_index=False.

[sfc-gh-nkrishna]

Can we add tests for this?

[sfc-gh-rdurrani]

Can we add tests for this?

I think there are already tests for this? Because in a lot of the groupby tests, we have a getitem test, so that checks that this works correctly. Would you like me to add some tests that check the types of SeriesGroupBy vs. DataFrameGroupBy?

[sfc-gh-nkrishna]

Can we add tests for this?

I think there are already tests for this? Because in a lot of the groupby tests, we have a getitem test, so that checks that this works correctly. Would you like me to add some tests that check the types of SeriesGroupBy vs. DataFrameGroupBy?

Yeah in general I think it would be helpful to have an associated test (an isinstance check sounds good to me) whenever there is a bug fix

[sfc-gh-nkrishna]

LGTM!

[sfc-gh-lmukhopadhyay]

LGTM!

[sfc-gh-helmeleegy]

Nice! Thanks, Rehan.