Pin alpine image used in release pipeline

[AlanGreene]

Changes

Related to tektoncd/plumbing#2197
/kind misc

Submitter Checklist

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

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
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• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[AlanGreene]

/test pull-tekton-pipeline-integration-tests

[AlanGreene]

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

[tekton-robot]

@AlanGreene: 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-beta-integration-tests
• /test pull-tekton-pipeline-build-tests
• /test pull-tekton-pipeline-integration-tests
• /test pull-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 pull-tekton-pipeline-go-coverage-df

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[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

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[afrittoli]

/lgtm

[AlanGreene]

/test pull-tekton-pipeline-beta-integration-tests

[afrittoli]

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

[tekton-robot]

@afrittoli: 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-beta-integration-tests
• /test pull-tekton-pipeline-build-tests
• /test pull-tekton-pipeline-integration-tests
• /test pull-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 pull-tekton-pipeline-go-coverage-df

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.