Add rekt tests for DefaultBrokerClass config

[Leo6Leo]

Problem
We need to add rekt (reconciler tests) for the DefaultBrokerClass configuration. The focus should be on validating that the default configuration works correctly with the recent changes.

Persona
Eventing Contributor

Exit Criteria

• Rekt tests for DefaultBrokerClass configuration are implemented
• Tests pass, confirming that the default configuration works as expected with new changes

Scope

• This test should focus on the default configuration
• Extensive corner cases are not required, as they will be covered by unit tests

Time Estimate
1 developer-day

Dependencies

• Blocked by: Broker class based defaults #7631 (needs to be merged first)

Additional Context

• The rekt tests implemented here should be focused and not cover many different corner cases, as those will be handled by unit tests to avoid expensive rekt tests.
• Once PR Broker class based defaults #7631 is merged, this task will be unblocked and ready for implementation.