The `# -*- coding: utf-8 -*-` headers were useful for Python 2, and
aren't needed for Python 3 where UTF-8 is the default.
yamllint support of Python 2 was dropped in early 2021, see commit
a3fc64d "End support for Python 2".
Let's drop these headers.
We'd like to disallow brackets and braces in our YAML, but there's a
catch: the only way to describe an empty array or hash in YAML is to
supply an empty one (`[]` or `{}`). Otherwise, the value will be null.
This commit adds a `non-empty` option to `forbid` for brackets and
braces. When it is set, all flow and sequence mappings will cause errors
_except_ for empty ones.
Add 'forbid' configuration parameters to the braces and brackets rules
to allow users to forbid the use of flow style collections, flow
mappings and flow sequences.
