arrow

GH-43153: [R] pull on a grouped query returns the wrong column (#43172)

### Rationale for this change

Fix a bug in our implementation of `pull` on grouped datasets

### What changes are included in this PR?

An additional test, the fix.

### Are these changes tested?

Yes, with the test I added to.

### Are there any user-facing changes?

Users will now get the expected behavior when using `pull` on grouped queries.

**This PR contains a "Critical Fix".**
* GitHub Issue: #43153

Lead-authored-by: Jonathan Keane <jkeane@gmail.com>
Co-authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Jonathan Keane <jkeane@gmail.com>