contrib/mklog.py: Fix issues reported by flake8

The testing infrastructure built by Martin Liška contains checking a
few python scripts in contrib witha tool flake8.  That tool recently
complains that:

  contrib/mklog.py:360:45: E711 comparison to None should be 'if cond is None:'
  contrib/mklog.py:362:1: E305 expected 2 blank lines after class or function definition, found 1

I'd like to silence these with the following, hopefully trivial,
changes.  However, I have only tested the changes by running flake8
again and running ./contrib/mklog.py --help.

Is this good for trunk?  (Or should I stop using flake8 instead?)

Thanks,

Martin

contrib/ChangeLog:

2023-10-03  Martin Jambor  <mjambor@suse.cz>

	* mklog.py (skip_line_in_changelog): Compare to None using is instead
	of ==, add an extra newline after the function.