PermissionError: PathSlicingObjStorage root "/srv/softwareheritage/objects" is not writable

Sentry Issue: SWH-OBJSTORAGE-27

PermissionError: PathSlicingObjStorage root "/srv/softwareheritage/objects" is not writable
(2 additional frame(s) were not displayed)
...
  File "/opt/swh/.local/lib/python3.10/site-packages/swh/objstorage/api/server.py", line 31, in w
    return f(*a, **kw)
  File "/opt/swh/.local/lib/python3.10/site-packages/swh/core/api/negotiation.py", line 153, in newf
    return f.negotiator(*args, **kwargs)
  File "/opt/swh/.local/lib/python3.10/site-packages/swh/core/api/negotiation.py", line 81, in __call__
    result = self.func(*args, **kwargs)
  File "/opt/swh/.local/lib/python3.10/site-packages/swh/core/api/__init__.py", line 582, in f
    ret = obj_meth(**kw)
  File "/opt/swh/.local/lib/python3.10/site-packages/swh/objstorage/backends/pathslicing.py", line 195, in check_config
    raise PermissionError(