Use Black stable to format python code

The first stable release of the Black code formatter, 22.1.0 [1] is now
available with a promise of code style stability for all versions
sharing the same major version number [2].

Set the requirements to 'black ~= 22.0' to get bug fix releases while
maintaining a stable code style.

[1] https://github.com/psf/black/releases/tag/22.1.0
[2] https://black.readthedocs.io/en/latest/the_black_code_style/index.html#stability-policy

Change-Id: I8b7843deff87464237a9214d4ea3bf18e4d987a1
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7406
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>