[fix] set .ssh folder permissions to 600

Fix YunoHost/issues#1770

src/yunohost/ssh.py

@@ -64,6 +64,7 @@ def user_ssh_add_key(username, key, comment):
             parents=True,
             uid=user["uid"][0],
         )
+        chmod(os.path.join(user["homeDirectory"][0], ".ssh"), 0o600)
 
         # create empty file to set good permissions
         write_to_file(authorized_keys_file, "")