[release-1.12] test refactorings

[knative-prow-robot]

This is an automated cherry-pick of #1640

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: knative-prow-robot, matzew

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (abb9d09) 79.40% compared to head (1e7bf9a) 79.40%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-1.12 #1641 +/- ## ============================================= Coverage 79.40% 79.40% ============================================= Files 41 41 Lines 1845 1845 ============================================= Hits 1465 1465 Misses 277 277 Partials 103 103 ```

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[matzew]

/test eventing-upgrade-tests

[matzew]

/lgtm