Python Dialog Button supported by PF_FILE is not fixed width

GIMP version: 2.10.8

Operating System: Windows 10 version 1809

Description of the bug

It is trivial, but please change the following contents.

The Button width shown by Python Menu register 'PF_FILE' or 'PF_FILENAME' must be fixed width.
When enlarge the dialog size, the button width is enlarged, too. :)