Update c_timestamp.pyx

Added missing dots

Author: ShaharNaveh

pandas/_libs/tslibs/c_timestamp.pyx

@@ -382,9 +382,9 @@ cdef class _Timestamp(datetime):
         result = f'{self.hour:02d}:{self.minute:02d}:{self.second:02d}'
 
         if self.nanosecond != 0:
-            result += f'{self.nanosecond + 1000 * self.microsecond:09d}'
+            result += f'.{self.nanosecond + 1000 * self.microsecond:09d}'
         elif self.microsecond != 0:
-            result += f'{self.microsecond:06d}'
+            result += f'.{self.microsecond:06d}'
 
         return result