fix: reject reserved result names in Task and StepAction validation

[ogulcanaydogan]

Changes

Fixes #10631.

entrypointer.go writes internal bookkeeping entries (Key: "ExitCode", Key: "StartedAt", Key: "Reason", with ResultType: InternalTektonResultType) into the same []result.RunResult termination message array as user-declared Task and Step results, distinguished only by ResultType.

If a Task or StepAction author declares a result named ExitCode, StartedAt, or Reason, the user result collides with the internal entry. Depending on ordering, the internal value may be overwritten, causing incorrect status reporting for the Step.

This adds a reserved-name check to TaskResult.Validate() and StepResult.Validate() (pkg/apis/pipeline/v1/result_validation.go), so these names are rejected at webhook validation time rather than silently colliding at runtime.

This is self-inflicted-confusion prevention only (the Task author controls their own result names) — no cross-tenant or security impact, per the issue's linked security advisory triage (closed as not a vulnerability).

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Release Notes

Task and StepAction results can no longer be named `ExitCode`, `StartedAt`, or `Reason`, since those names collide with internal bookkeeping results written by the entrypointer.

[ogulcanaydogan]

/kind bug

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.73%. Comparing base (61e0221) to head (2cd45d5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10824   +/-   ##
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  Coverage   90.73%   90.73%           
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  Files         297      297           
  Lines       22569    22573    +4     
=======================================
+ Hits        20478    20482    +4     
  Misses       2089     2089           
  Partials        2        2           

Flag	Coverage Δ
unit-tests	90.73% <100.00%> (+<0.01%)	⬆️

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