Fix loading of per-cluster size constants from v2 spexical files

src/spexipy/spexical.py

@@ -53,7 +53,7 @@ class SpeXICAL:
         else:
             cluster_cal_struct = struct.Struct('<f')
             for i in range(self._cluster_cal_count):
-                offset = cluster_cal_struct.unpack_from(self._file.read(cluster_cal_struct.size))
+                offset, = cluster_cal_struct.unpack_from(self._file.read(cluster_cal_struct.size))
                 self.cluster_calibrations.append(offset)
 
         self.dark_offset = self._load_frame(np.float32)