Fast follow to #42050

[BillWagner]

Fix redirects that caused warnings.

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Internal previews

📄 File	🔗 Preview link
docs/core/extensions/dependency-injection-basics.md	docs/core/extensions/dependency-injection-basics
docs/csharp/how-to/index.md	docs/csharp/how-to/index
docs/csharp/language-reference/keywords/event.md	docs/csharp/language-reference/keywords/event
docs/csharp/programming-guide/events/how-to-subscribe-to-and-unsubscribe-from-events.md	docs/csharp/programming-guide/events/how-to-subscribe-to-and-unsubscribe-from-events
docs/csharp/programming-guide/events/index.md	docs/csharp/programming-guide/events/index
docs/standard/serialization/binaryformatter-migration-guide/functionality-reference.md	docs/standard/serialization/binaryformatter-migration-guide/functionality-reference
docs/standard/serialization/binaryformatter-migration-guide/winforms-applications.md	docs/standard/serialization/binaryformatter-migration-guide/winforms-applications
docs/standard/serialization/binaryformatter-migration-guide/wpf-applications.md	docs/standard/serialization/binaryformatter-migration-guide/wpf-applications