Suppress optional workload notices with dotnet new --no-update-check

[Copilot]

dotnet new --no-update-check suppressed NuGet update checks but still reported newer built-in packages from providers such as Optional workloads.

• Behavior

  • Skip built-in package availability checks when --no-update-check is specified.
  • Preserve existing notices when update checks are enabled.

• Coverage

  • Add a regression test for a manually installed template package overriding a newer built-in package.

• Fixes dotnet new --no-update-check does not suppress Optional workloads provider notice #55386

[azure-pipelines]

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