get_by_label_all only works after sync_attributes

[francescalb]

When making a new entity it is not immediately available with get_by_label_all

from ontopy import get_ontology
batt = get_ontology('https://raw.githubusercontent.com/BIG-MAP/BattINFO/dev/battinfo.ttl').load()
batt.new_entity('Tull',batt.Electrolyte)

Now:
batt.get_by_label('Tull') returns battinfo.Tull, but `batt.get_by_label_all('Tull') return an empty list.
Ater running batt.sync_attributes(), Tull is findable also with get_by_label_all.

New concepts should be available directly from get_by_label_all before sync_attributes.