Fix unreachable code in TestReconcileCancelledFailsTaskRunCancellation

[abayer]

Changes

Code in TestReconcileCancelledFailsTaskRunCancellation was never going to be reached - it was getting a value from a map and fataling if the key wasn't present, and then the actual test logic for that value was in the same block as the t.Fatalf. I rearranged that, and also made the test logic for the value be valid - it was expecting test-pipelines as the value, but the value was actually always test-pipeline (singular!).

/kind cleanup

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[pritidesai]

thank you @abayer
/lgtm