`ARENDAL CN 007..012` and `ARENDAL T1`

[VladimirAlexiev]

statnett/Nordic44#62 lists about 8 PSRs with the same name but
different URNs in Nordic (?mrid_n) vs Telemark (?mrid_t):
ARENDAL CN 007..012 and ARENDAL T1

Please make the URNs the same to increase correlation between the two datasets