Remove comparing serviceaccount in tests

[piyush-garg]

This will remove comparing service account in eventlistener create test as the default serviceaccount can be different on different platforms like operator on OpenShift

This remove the serviceaccount field from expected output and also add ignore field in cmp.Diff

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Release Notes

Remove comparing serviceaccount in tests

[khrm]

/kind cleanup

[tekton-robot]

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