Updated function signature in pxd file.

Author: Victor

pandas/_libs/tslibs/timedeltas.pxd

@@ -3,7 +3,7 @@
 from numpy cimport int64_t
 
 # Exposed for tslib, not intended for outside use.
-cdef parse_timedelta_string(object ts, specified_unit=*)
+cdef parse_timedelta_string(object ts, object specified_unit=None)
 cpdef int64_t cast_from_unit(object ts, object unit) except? -1
 cpdef int64_t delta_to_nanoseconds(delta) except? -1
 cpdef convert_to_timedelta64(object ts, object unit)