[web/views] avoid propagation of NoSelectableObject in some case of inlined relations / permissions When selecting an inlined creation form, we should catch the NoSelectable exception that will be raised if the user cannot add entities of the target type (this is not and cannot be verified earlier) or if some other custom selector prevents the form from being selected. Closes #6510921

[server/test] bit of PEP8

[migration] don't attempt to carry over values when renaming a computed relation Without the fix in migractions.py, the introduced test crashes with an operational error because of an attempt to write to a non-existing relation table (computed relations are not materialized). Closes #6304946