Update shebang directive to use portable env format

[Copilot]

Summary

The #! preprocessor directive example used a hardcoded dotnet path that only works on specific installations. Updated to use /usr/bin/env for portability across Unix and macOS distributions.

Changed:

• Shebang from #!/usr/local/share/dotnet/dotnet run to #!/usr/bin/env dotnet run
• Explanation text to clarify the /usr/bin/env locates dotnet in PATH

Fixes #49924

Original prompt

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This section details on the original issue you should resolve

<issue_title>The #! directive should be #!/usr/bin/env dotnet</issue_title>
<issue_description>### Type of issue

Outdated article

Description

See #49923

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/language-reference/preprocessor-directives.md

Document Version Independent Id

501be68d-5ad0-18d9-8958-54215bb57fc0

Platform Id

84295fdd-62d6-f945-9adf-cc56ef16aa70

Article author

@BillWagner

Metadata

• ID: 716913e5-dbbe-bdb0-909a-4d8c2dc7be97
• PlatformId: 84295fdd-62d6-f945-9adf-cc56ef16aa70
• Service: dotnet-csharp
• Sub-service: lang-reference

Related Issues</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes The #! directive should be #!/usr/bin/env dotnet #49931

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docs/csharp/language-reference/preprocessor-directives.md	docs/csharp/language-reference/preprocessor-directives

[BillWagner]

This is ready for final review.

[Copilot]

Pull Request Overview

This PR updates the shebang directive example in the C# preprocessor directives documentation to use a portable format that works across different Unix and macOS distributions.

Key changes:

• Updated shebang from hardcoded path #!/usr/local/share/dotnet/dotnet run to portable #!/usr/bin/env dotnet run
• Enhanced explanation to clarify how /usr/bin/env locates the dotnet executable in PATH