Fix csharp workflow variables inconsistent.

[IcedMango]

Section: Workflow Variables and Input

Problem: The function and example are inconsistent: Variables / Variable

Document URL: Workflow Variables and Input

[vercel[bot]]

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Name	Status	Preview	Comments	Updated (UTC)
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[vercel[bot]]

@IcedMango is attempting to deploy a commit to the Elsa Workflows Team on Vercel.

A member of the Team first needs to authorize it.

[IcedMango]

@dotnet-policy-service agree