🛂(backend) remove svg from unsafe

We added content-security-policy on nginx.
It should be safe to allow svg files now.
We remove the svg file from the unsafe
attachments list. We adapt the tests accordingly.

src/backend/impress/settings.py

@@ -210,7 +210,6 @@ class Base(Configuration):
         "application/x-ms-regedit",
         "application/x-msdownload",
         "application/xml",
-        "image/svg+xml",
     ]
 
     # Document versions