[fix] format.python: regexp argument '--include' in BLACK_TARGETS

--include TEXT

  A regular expression that matches files and directories that should be
  included on recursive searches. An empty value means all files are included
  regardless of the name.  ...  Exclusions are calculated first, inclusions
  later.  [default: \.pyi?$]

Closes: https://github.com/searxng/searxng/issues/1142


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>