fix: panic in v1beta1 matrix validation for invalid result refs

[mathur07]

This fix applies the same safety check that was added to v1 pipelines in PR #8089. The validateMatrixedPipelineTaskConsumed function was panicking when encountering invalid variable substitutions like "$(tasks)-$(tasks.echo-result.results.output)" because it tried to access subExpressions[1] without first checking if the expression was a valid result reference.

The fix adds a check to skip expressions that don't look like result references before attempting to parse them, preventing the panic and allowing the webhook to return a proper validation error instead.

Related: #8089

Changes

Submitter Checklist

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Release Notes

Resolved an issue where Pipelines with invalid result references in matrix parameters would cause a panic during validation (v1beta1 API)

[mathur07]

/kind fix

[tekton-robot]

@mathur07: The label(s) kind/fix cannot be applied, because the repository doesn't have them.

In response to this:

/kind fix

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.

[mathur07]

/ok-to-test

[mathur07]

/retest

[vdemeester]

TestExamples/v1/taskruns/dind-sidecar is consistently failing on this PR 🤔

[mathur07]

The test failure appears to be a Docker Hub rate-limiting issue.

[aThorp96]

CI will likely be resolved with #9139

[aThorp96]

/lgtm

[waveywaves]

/retest

[tekton-robot]

New changes are detected. LGTM label has been removed.

[afrittoli]

/kind bug

[afrittoli]

SRVKP-9204 does not seem to be publicly accessible - it requires a RedHat login.

[vdemeester]

Arf, because it's coming from a support request... @mathur07 we should only link to publicly available issues 👼🏼

[mathur07]

@vdemeester @aThorp96 can you please help with a /retest

[aThorp96]

Looks good to me. Please add release notes and complete the submitter checklist in the PR description 🙏🏼

[tekton-robot]

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