Fix formatting for dotnet shebang code example

[WeihanLi]

Summary

This pull request makes a minor documentation fix to improve clarity in the C# file-based program tutorial.

• Documentation: Corrected the formatting of the shebang example by wrapping #!/usr/bin/env dotnet in backticks for proper code highlighting.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/fundamentals/tutorials/file-based-programs.md	Tutorial: Build file-based C# programs

[Copilot]

Pull Request Overview

This PR improves documentation formatting in the C# file-based programs tutorial by wrapping the shebang directive #!/usr/bin/env dotnet in backticks for proper inline code highlighting, which aligns with Markdown documentation standards.

• Adds backticks around #!/usr/bin/env dotnet to format it as inline code

[BillWagner]

This LGTM and I'll now.