Disable Crossgen2 Json CG2 composite job

[LoopedBard3]

Disables the CG2 composite profile in build/crossgen2-scenarios.yml (used by both benchmarks-ci-01 and benchmarks-ci-02) by flipping its condition to 'false', matching the pattern already used for the CG2 composite avx2 profile.

Why

The Json CG2 composite job has been consistently failing during the crossgen2 composite publish step with:

error : Unhandled exception. ILCompiler.CodeGenerationFailedException: Code generation failed for method
        'Async variant: [Microsoft.AspNetCore.Components.Server]
         Microsoft.AspNetCore.Components.Server.Circuits.RemoteJSDataStream.CompletePipeAndDisposeStream(Exception)'
 ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
    at Internal.IL.Stubs.ILStubMethodIL.GetObject(...)
    at Internal.JitInterface.CorInfoImpl.HandleToModuleToken(...)
    at Internal.JitInterface.CorInfoImpl.ComputeMethodWithToken(...)
    at Internal.JitInterface.CorInfoImpl.getCallInfo(...)
    ...
error NETSDK1096: Optimizing assemblies for performance failed. ...

On the Windows leg this has additionally caused crank to hang/get stuck, which then prevents all of the remaining jobs in the pipeline from running. Disabling the profile keeps the rest of the crossgen2 scenarios (Default, CG2 non-composite) running while we wait for the underlying crossgen2 issue to be resolved.

Scope

• Only the CG2 composite profile entry under the shared crossgen2-scenarios.yml template is changed; both benchmarks-ci-01.yml and benchmarks-ci-02.yml consume this template, so the job is disabled in both pipelines with a single change.
• Default, CG2 non-composite, and the already-disabled CG2 composite avx2 profiles are unchanged.

Marking as draft for review.

[Copilot]

Pull request overview

This PR disables the CG2 composite crossgen2 profile in the shared build/crossgen2-scenarios.yml template to prevent recurring crossgen2 composite publish failures (and associated Windows crank hangs) from blocking the rest of the CI pipeline.

Changes:

• Disabled the CG2 composite profile by setting its condition to 'false'.
• Added inline documentation explaining why the profile is disabled (failure + pipeline impact).

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