"remote authentication required but no callback set" in pull after upgrading from 0.28 to 0.29

@bording we get the error "remote authentication required but no callback set" after upgrading from 0.28 to 0.29 when connecting to a company internal azure devops server.

This works great with the old version using windows authentication.

Reproduction steps

• connect to a company internal azure devops server via windows authentication

      Signature signature = GetSignature();
      PullOptions pullOptions = new()
      {
        MergeOptions = new() { FileConflictStrategy = CheckoutFileConflictStrategy.Theirs }
      };
      MergeResult mergeResult = Commands.Pull(Repository, signature, pullOptions);

Expected behavior

Success

Actual behavior

LibGit2Sharp.LibGit2SharpException
HResult=0x80131500
Message=remote authentication required but no callback set
Source=LibGit2Sharp
StackTrace:
at LibGit2Sharp.Core.Ensure.HandleError(Int32 result) in /_/LibGit2Sharp/Core/Ensure.cs:line 154

Version of LibGit2Sharp (release number or SHA1)

0.29

Operating system(s) tested; .NET runtime tested

Windows 11, .NET 4.8

Seems to be related to #2065 and #2087

Comienza con la llamada Pull y la ruta de error en Core/Ensure.cs en la línea 154; después, compara el comportamiento de autenticación entre las versiones 0.28 y 0.29. Revisa los issues relacionados #2065 y #2087 y reproduce el problema en el servidor interno de Azure DevOps en Windows con .NET 4.8. Se considera terminado cuando el pull mostrado se ejecuta correctamente usando la autenticación de Windows sin la missing-callback exception.