[vulncheck ] Use append for SCOPE_SOFTWARE in vulncheck (nistnvd2 source)

[giacomovitangeli]

Proposed changes

• Replace extend() with append() to correctly add the object without string iteration.

Related issues

• This pull request fixes an issue in the vulncheck connector (nistnvd2 source) where the SCOPE_SOFTWARE data was not being handled correctly. The error occurred because extend was used to add a single relationship object, which caused Python to iterate over the object (string iteration).
• [vulncheck ] Use append for SCOPE_SOFTWARE in vulncheck (nistnvd2 source) #3524

[helene-nguyen]

Thanks for this :)