Cleanup resources from DeploymentFailure upgrade test

[mgencur]

Proposed Changes

• Clean up the resources when the test ends (webhook, knative service) as the namespace might be used for running other tests afterwards (e.g. other Serving E2E tests or upgrade tests for cluster-upgrades)

Release Note

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.77%. Comparing base (c2d0af1) to head (f7b4f21).
Report is 117 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15227      +/-   ##
==========================================
+ Coverage   84.11%   84.77%   +0.66%     
==========================================
  Files         213      218       +5     
  Lines       16783    13473    -3310     
==========================================
- Hits        14117    11422    -2695     
+ Misses       2315     1685     -630     
- Partials      351      366      +15     

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[ReToCode]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mgencur, ReToCode

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