textproc/py-extract-msg: update to 0.40.0

ChangeLog: https://github.com/TeamMsgExtractor/msg-extractor/blob/v0.40.0/CHANGELOG.md

* Added new code to handle injection of text into the RTF body. For
  many cases, this will be much more effective as it relies on ensuring
  that it is in the main group and past the header before injection. It
  is not currently the first choice as it doesn't have proper respect
  for encapsulated HTML, however it will replace some of the old methods
  entirely. Solving this issue was done through the use of a few
  functions and the internal _rtf module. This module in it's entirety
  is considered to be implementation details, and I give no guarantee
  that it will remain in it's current state even across patch
  versions. As such, it is not recommended to use it outside of the
  module.
* Changed MessageBase.rtfEncapInjectableHeader and
  MessageBase.rtfPlainInjectableHeader from str to bytes. They always
  get encoded anyways, so I don't know why I had them returning as str.
* Updated minimum Python version to 3.8 as 3.6 has reached end of
  support and 3.7 will reach end of support within the year.
* Updated information in README.

PR:		270392
Reported by:	Jesús Daniel Colmenares Oviedo <DtxdF@disroot.org>