Co-authored-by: sirosen <sirosen@users.noreply.github.com>

- Add a TOML module alongside the YAML and JSON5 ones, with an enabled
  flag and a "missing support message" like JSON5
- Refactor the JSON5 unit testing to be more general "optional parser"
  testing
- Add an acceptance test for successful TOML parsing and validation
- Add `-tomli` to tox factors in tox.ini and CI
- Add TOML to optional parsers doc

In order to support `tomli` behavior, the `open()` call for instance
files had to switch from `encoding="utf-8"` to using `"rb"` mode. This
should not have any user-facing impact, but it is noted in the
changelog to improve visibility in case there are unexpected issues.

One fix is a `type:ignore` comment for a bad annotation which was
introduced and then fixed. The other is the addition of an `if` check
for an optional list which was being treated as non-optional.

updates:
- [github.com/python-jsonschema/check-jsonschema: 0.15.0 → 0.15.1](0.15.0...0.15.1)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Co-authored-by: sirosen <sirosen@users.noreply.github.com>

Improved format support includes better specifying which checkers to
use based on the JSON Schema draft/version in use. Without this,
attempting to format-validate TOML data which parses as datetime or
time types is difficult, as the draft03 time format checker was
used by default.

In order to better exercise this behavior, `jsonschema[format]` is
added to the tox matrix and run with and without the TOML tests.

After the TOML and formatting changes, there were a few typing
mistakes introduced. Notably TextIO switched to BinaryIO in instance
loaders.

Also, improve comments on toml datetime conversion, and cleanup
"schema_attr" to be named "schema_dialect" for clarity.

* [vendor-schemas] automated update

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: sirosen <sirosen@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Tests behavior when `jsonschema[format]` is installed.

After a schema is downloaded in the vendor-schemas job, it could be
fixed by pre-commit.ci automatically. The result is an extra push and
noise on the auto-update PR. It's better if the CI job automatically
runs pre-commit on the results (or if the vendored schemas were
ignored under pre-commit; nearly equivalent).
This also ensures that if the only change is that the downloaded
schema reverts the autofixing done under pre-commit, nothing will be
recorded as changed.

Update the gitlab schema by running `make vendor-schemas`.

- Update to 'ruamel.yaml' v0.17.21
- Switch from 'pytest-cov' to plain 'coverage'