fix: Non-admin users can create invites

[khvn26]

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Changes

This prevents non-admin users from creating invites using the organisations/{org-id}/invite endpoint.

How did you test this code?

Added a unit test for the scenario.

[vercel]

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3 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)			Sep 23, 2024 3:18pm
flagsmith-frontend-preview	⬜️ Ignored (Inspect)			Sep 23, 2024 3:18pm
flagsmith-frontend-staging	⬜️ Ignored (Inspect)			Sep 23, 2024 3:18pm

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-4653	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-e2e:pr-4653	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-frontend:pr-4653	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-api:pr-4653	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-4653	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-4653	Finished ✅	Results ✅

[github-actions]

Uffizzi Preview deployment-56551 was deleted.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.18%. Comparing base (b4d3310) to head (5841010).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4653   +/-   ##
=======================================
  Coverage   97.17%   97.18%           
=======================================
  Files        1163     1163           
  Lines       40280    40288    +8     
=======================================
+ Hits        39144    39152    +8     
  Misses       1136     1136           

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