fix(parser): handle self-repository references in comparison parser

[nobbs]

Accept $/ self-repository references consistently when action-manifest parser comparison is enabled.

The newer parser previously emitted a false validation annotation and converted this reference differently from the legacy parser. This aligns validation and conversion with the legacy behavior, with a regression test covering comparison mode.

Fixes #4706

[Copilot]

🔵 Needs a closer look

The regression test should directly verify the new-parser converted repository reference.

Pull request overview

Fixes parser comparison handling for $/... self-repository references by aligning validation and conversion with legacy behavior.

Changes:

• Accepts valid self-repository references during validation.
• Converts references consistently in comparison mode.
• Adds composite-action regression coverage.

File summaries

File	Summary
src/Test/TestData/self_repository_composite_action.yml	Adds composite-action test data using a self-repository reference.
src/Test/L0/Worker/ActionManifestParserComparisonL0.cs	Adds comparison regression coverage, but assertions currently inspect only the legacy result.
src/Sdk/WorkflowParser/Conversion/WorkflowTemplateConverter.cs	Excludes valid self-repository references from validation.
src/Runner.Worker/ActionManifestManagerWrapper.cs	Converts self-repository references consistently.

Review details

Suppressed comments (1)

src/Test/L0/Worker/ActionManifestParserComparisonL0.cs:125

• These assertions inspect the legacy result: ActionManifestManagerWrapper.Load always returns the legacy result, while CompareCompositeExecution only compares step count and outputs. The test would therefore still pass if the new-parser path in ConvertToLegacySteps (including the new $/ mapping) produced a different repository reference. Please compare or directly assert the converted new step reference so the regression covers both changes.

                var reference = Assert.IsType<GitHub.DistributedTask.Pipelines.RepositoryPathReference>(nestedAction.Reference);
                Assert.Equal(GitHub.DistributedTask.Pipelines.PipelineConstants.SelfRepositoryAlias, reference.RepositoryType);
                Assert.Equal("actions/nested", reference.Path);
                Assert.False(_ec.Object.Global.HasActionManifestMismatch);

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Lite

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[nobbs]

Closing as a duplicate of #4669, which contains the same production fix and broader regression coverage for self-repository references in parser comparison.