L2SS-1149: fix observation attribute type

Closes L2SS-1149

tangostationcontrol/tangostationcontrol/devices/observation.py

@@ -54,7 +54,7 @@ class Observation(LOFARDevice):
     antenna_mask_R = attribute(
         dtype=(numpy.int64,), max_dim_x=MAX_ANTENNA, access=AttrWriteType.READ
     )
-    filter_R = attribute(dtype=numpy.str, access=AttrWriteType.READ)
+    filter_R = attribute(dtype=str, access=AttrWriteType.READ)
     saps_subband_R = attribute(
         dtype=((numpy.uint32,),),
         max_dim_x=N_beamlets_ctrl,
@@ -62,13 +62,13 @@ class Observation(LOFARDevice):
         access=AttrWriteType.READ,
     )
     saps_pointing_R = attribute(
-        dtype=((numpy.str,),),
+        dtype=((str,),),
         max_dim_x=N_point_prop,
         max_dim_y=N_beamlets_ctrl,
         access=AttrWriteType.READ,
     )
     tile_beam_R = attribute(
-        dtype=(numpy.str,), max_dim_x=N_point_prop, access=AttrWriteType.READ
+        dtype=(str,), max_dim_x=N_point_prop, access=AttrWriteType.READ
     )
     first_beamlet_R = attribute(dtype=numpy.int64, access=AttrWriteType.READ)