[API] Robot results import: New Test version always created when no Xray Enterprise

When importing Robot results to a Test whose default Test version has a custom generic definition and Xray Enterprise is not installed, a new Test version is always created.

Steps to reproduce:

1. Create a Test with a generic Test Type and add a custom generic definition (e.g. a table with some data).
   NOTE: This custom generic definition must be different from the one generated by the Robot results that will be imported.
2. Import Robot results to that Test (use a tag with the Test issue key).
   Expected result: Should use the default Test version, since Xray Enterprise is not installed.
   Actual result: A new Test version is created, even if Xray Enterprise is not installed.
3. Import again the same Robot results to the same Test.
   Expected result: Should use the default Test version, since Xray Enterprise is not installed.
   Actual result: A new Test version is created, even if Xray Enterprise is not installed and there is a Test version with the same generic definition.