[InterNetNews/inn] 1dfbc3: black: Remove the experimental flag

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 1dfbc322df322be223c33aab863cb4011cbd2a07
      https://github.com/InterNetNews/inn/commit/1dfbc322df322be223c33aab863cb4011cbd2a07
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2022-02-19 (Sat, 19 Feb 2022)

  Changed paths:
    M Makefile

  Log Message:
  -----------
  black: Remove the experimental flag

The Black project has just released their first non-beta release!
Starting with Black 22.1.0, a new stability policy applies.

The --experimental-string-processing no longer exists, so we just
remove it.  It is no longer necessary (though experimental style could now
be enabled with --preview, it will be included in the first release of the
next year, if kept).