arrow

MINOR: [R] Fix .lintr config file for updated lintr dependency (#38639)

### Rationale for this change

The lint CI job is failing because an update to a dependency of lintr now does more strict DCF checking on the .lintr file

### What changes are included in this PR?

The 'license' field was wrapped in quotes so that .lintr passes validation

### Are these changes tested?

Yes, by existing CI job

### Are there any user-facing changes?

No

Authored-by: Dewey Dunnington <dewey@voltrondata.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>