Fix hardcoded knative-eventing namespace in eventingControllerSAName

[vaidikcode]

Fixes #8407

Proposed Changes

-:bug: Fix bug

• changed the hardcoded value as discussed in Unable to deploy eventing in different namespace because of hardcoded namespace #8407

Pre-review Checklist

• At least 80% unit test coverage
• E2E tests for any new behavior
• Docs PR for any user-facing impact
• Spec PR for any new API feature
• Conformance test for any change to the spec

Release Note

Docs

[knative-prow]

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[knative-prow]

Hi @vaidikcode. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[pierDipi]

https://github.com/knative/eventing/actions/runs/12930925415/job/36063811420?pr=8425

Various

panic: The environment variable "SYSTEM_NAMESPACE" is not set
	
	If this is a process running on Kubernetes, then it should be using the downward
	API to initialize this variable via:
	
	  env:
	  - name: SYSTEM_NAMESPACE
	    valueFrom:
	      fieldRef:
	        fieldPath: metadata.namespace

We would need to update the tests

[vaidikcode]

How should we approach this? Should I keep it simple with:

var eventingControllerSAName = fmt.Sprintf("system:serviceaccount:%s:eventing-controller", system.Namespace())

Should I also start working on tests?