[Task] Increase test coverage of addons

[Himangini]

Description

Increase test coverage for addons.

There are a few places tests are missing. See https://github.com/weaveworks/eksctl/issues/5570, https://github.com/weaveworks/eksctl/pull/5571, https://github.com/weaveworks/eksctl/pull/5458 These PRs don't add any tests and verifying this functionality is purely based on manual testing