[6.13.z] Fix get_downloads_list which is causing save_downloaded_file to fail

[Satellite-QE]

Cherrypick of PR: #1098

Fix get_downloads_list which is causing save_downloaded_file to fail. Fixed issue and removed some unnecessary code.

tests/foreman/ui/test_rhcloud_inventory.py:209: in test_rh_cloud_inventory_settings
    report_path = session.cloudinventory.download_report(org.name)
../../lib64/python3.11/site-packages/airgun/entities/cloud_inventory.py:43: in download_report
    return self.browser.save_downloaded_file()
../../lib64/python3.11/site-packages/airgun/browser.py:430: in save_downloaded_file
    file_uri = files[0]
E   IndexError: list index out of range

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/ui/test_rhcloud_inventory.py -k test_rh_cloud_inventory_settings