Fix reference to IsPrime method in unit testing docs (#49648)

Corrected the reference to the method in the PrimeService.cs file for clarity.

Author: snehansh

docs/core/testing/unit-testing-csharp-with-nunit.md

@@ -176,7 +176,7 @@ Instead of creating new tests, apply this attribute to create a single data-driv
 
 [!code-csharp[Sample_TestCode](~/samples/snippets/core/testing/unit-testing-using-nunit/csharp/PrimeService.Tests/PrimeService_IsPrimeShould.cs?name=Sample_TestCode)]
 
-Run `dotnet test`, and two of these tests fail. To make all of the tests pass, change the `if` clause at the beginning of the `Main` method in the *PrimeService.cs* file:
+Run `dotnet test`, and two of these tests fail. To make all of the tests pass, change the `if` clause at the beginning of the `IsPrime` method in the *PrimeService.cs* file:
 
 ```csharp
 if (candidate < 2)