[server/sources] fix name error in eid_type_source_pre_131 i.e. the eid_type_source implementation used when some pre 3.13.1 database is detected. Regression from 5fbdbbe51867.

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')