front: add trigram of new selected op

Signed-off-by: SarahBellaha <sarah.bellaha@sncf.fr>

front/src/applications/stdcm/components/StdcmForm/StdcmOperationalPoint.tsx

@@ -82,6 +82,7 @@ const StdcmOperationalPoint = ({ point, opPointId, disabled }: StdcmOperationalP
           ch: p.ch,
           uic: p.uic,
           coordinates: p.geographic.coordinates,
+          trigram: p.trigram,
         }
       : { name: undefined, ch: undefined, uic: -1, coordinates: undefined };
     dispatch(updateStdcmPathStep({ id: point.id, updates: newPoint }));