Fix for Create PipelineRun specifying ServiceAccount with v1 API

[AlanGreene]

Changes

Resolves #3285
/kind bug

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Release Notes

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[AlanGreene]

/retest

[AlanGreene]

Some of the tests are timing out, seems like it's due to heavier load than normal on the test clusters causing delays starting runs / pulling images. Not related to the Dashboard itself.
/retest

[AlanGreene]

/retest

[briangleeson]

/lgtm

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