fix(mtd): retrieve af even if actors association impossible

Commit the retrieval of an acquisition framework to the database before processing the retrieval and association of its actors, i.e. the execution of `associate_actors`.
This prevents the retrieval of the AF not be to committed in the case there happen to be issues in the execution of `associate_actors`

backend/geonature/core/gn_meta/mtd/__init__.py

@@ -206,6 +206,8 @@ def process_af_and_ds(af_list, ds_list, id_role=None):
             add_unexisting_digitizer(af["id_digitizer"] if not id_role else id_role)
             user_add_total_time += time.time() - start_add_user_time
         af = sync_af(af)
+        # Commit here to retrieve the AF even if the association of actors that follows is to fail
+        db.session.commit()
         # If the AF has not been retrieved, associated actors cannot be retrieved either
         #   and thus we continue to the next AF
         if not af: