fix: createEnterpriseGroup response camelCase

[marlonkeating]

This change fixes an issue with group creation introduced in #1426.

Testing Instructions

• Go to the admin-portal repo, pull down branch, and run npm run start:stage
• Navigate to https://localhost.stage.edx.org:1991/alc-general/admin/people-management
• Click 'Create group'
• Add name, members, and click 'Create'
• Verify group is created with learners populated and no error messages

For all changes

• Ensure adequate tests are in place (or reviewed existing tests cover changes)

Only if submitting a visual change

• Ensure to attach screenshots
• Ensure to have UX team confirm screenshots

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.43%. Comparing base (d5fef09) to head (a39c80e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1433   +/-   ##
=======================================
  Coverage   86.43%   86.43%           
=======================================
  Files         660      660           
  Lines       14931    14932    +1     
  Branches     3171     3108   -63     
=======================================
+ Hits        12905    12906    +1     
- Misses       1956     1962    +6     
+ Partials       70       64    -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.