Importing scans fails for Generic Findings Import due to lack of file extension

[sarahgibs]

The upload_scan method does not specify a file name, leaving requests to use the generic value of 'file' in the multipart form upload. Recent changes to DefectDojo have made it so the Generic Findings Import no longer accepts a filename without a file extension. The requests sent via the v2 api fail with a 400 error.

`--dc1b35f1cdc7acb8055be35b6168dd63
Content-Disposition: form-data; name="file"; filename="file"

Date,Title,CweId,CVE,Url,Severity,Description,Mitigation,Impact,References,Active,Verified,FalsePositive,Duplicate,CVSSV3`