Skip validation for deletion of v1 task

[lbernick]

Changes

This commit bypasses v1 Task validation if the Task is being deleted.
This allows Tasks to be deleted if a new version of Tekton Pipelines is applied
that makes them invalid.

/kind bug

Submitter Checklist

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

• n/a Has Docs included if any changes are user facing
• n/a Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including
  functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• n/a Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings)
• n/a Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[lbernick]

FYI @vdemeester @JeromeJu

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

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• pkg/apis/OWNERS [vdemeester]

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[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/apis/pipeline/v1/task_validation.go	97.6%	97.1%	-0.4

[lbernick]

/retest

[lbernick]

/test check-pr-has-kind-label

[tekton-robot]

@lbernick: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test pull-tekton-pipeline-alpha-integration-tests
• /test pull-tekton-pipeline-build-tests
• /test pull-tekton-pipeline-integration-tests
• /test tekton-pipeline-unit-tests

The following commands are available to trigger optional jobs:

• /test pull-tekton-pipeline-go-coverage

Use /test all to run all jobs.

In response to this:

/test check-pr-has-kind-label

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[abayer]

/lgtm