fix(unit-testing): add correct files pattern in karma.conf.js when the project has nsconfig file

[Fatme]

Rel to: #4071

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• Tests for the changes are included.

What is the current behavior?

tns test <platform> does not execute any unit tests when the project has nsconfig file

What is the new behavior?

tns test <platform> executes unit tests when the project has nsconfig file