Handle forbidden error when checking for knative

What does this MR do?

This change handles a 403 when the knative-serving namespace doesn't exist.

Fixes #119379 (closed) Relates to #55246 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
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• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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