Don't modify the lister cache's copy.

[mattmoor]

/kind bug

Fixes: #4179

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Docs included if any changes are user facing
• Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including
  functionality, content, code)
• Release notes block below has been filled in or deleted (only if no user facing changes)

Release Notes

NONE

[mattmoor]

I'm not thrilled at the idea of discarding the error here either, but I figured it was worth leaving that alone for this change...

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/pipelinerun/pipelinerun.go	82.7%	82.8%	0.0

[mattmoor]

Ok, if I'm being really honest, I'm not a fan of any aspect of how the pipeline is handling retries by messing with another controller's resource's status to recycle it instead of just creating new taskruns 😂

[imjasonh]

I'd love some more systematic way to avoid this fwiw, identifying and fixing these by hand isn't going to scale. 🤔

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: imjasonh

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [imjasonh]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[mattmoor]

@imjasonh There is one! 😉 The knative table testing framework checks for this, which I think has effectively eliminated this from our controllers, but Tekton never adopted that because it landed around/after the split 😞

It'd be a pretty big undertaking, which I probably can't sign up for, but I'd be happy to consult, and I'm sure the Knative folks would be willing to field questions, since most of Knative is using it.

[mattmoor]

Here's where we do it, fwiw: https://github.com/knative/pkg/blob/b558677ab03404ed118ba3e179a7438fe2d8509a/reconciler/testing/table.go#L390-L394

[ghost]

/lgtm