[6.15.z] Fix upload_manifest to handle case where manifest.content is…

… not set (SatelliteQE#13834)

robottelo/host_helpers/satellite_mixins.py

@@ -146,7 +146,7 @@ def upload_manifest(self, org_id, manifest=None, interface='API', timeout=None):
 
         """
         if not isinstance(manifest, bytes | io.BytesIO):
-            if manifest.content is None:
+            if not hasattr(manifest, 'content') or manifest.content is None:
                 manifest = clone()
         if timeout is None:
             # Set the timeout to 1500 seconds to align with the API timeout.