Update graphviz requirement from <=0.18 to <=0.21

[dependabot]

Updates the requirements on graphviz to permit the latest version.

Changelog

Sourced from graphviz's changelog.

Version 0.21

Drop Python 3.8 support (end of life 7 Oct 2024).

Tag Python 3.13 support.

Add support for format='svg_inline', available since upstream Graphviz 10.0.1. Produces header-less SVG suitable for inlining into HTML (see https://www.graphviz.org/docs/outputs/svg/).

Switch project to pyproject.toml and build to python -m build) (https://build.pypa.io). This changes the source distribution formar from .zip to PEP 625 compliant .tar.gz (https://peps.python.org/pep-0625/).

Version 0.20.3

Revert improvements to the internal tools.deprecate_positional_args() decorator that caused false positive PendingDeprecationWarning: The signature of ... will be reduced warnings that have been misinterpreted in the 0.20.2 release process.

Version 0.20.2

Drop Python 3.7 support (end of life 27 Jun 2023).

Tag Python 3.11 and 3.12 support.

Add caveat about labe escaping/quoting to .node() and .render() API docs.

Document that doctest_skip_exe() lines in doctest should be ignored.

Improve internal tools.deprecate_positional_args() decorator and fix incorect test assertion.

Update GitHub actions.

Pin pytest test dependency to <8.1 as a workaround for import file mismatch error related to conftest.py files, in pytest 8.1.1, see pytest-dev/pytest#12123.

Version 0.20.1

... (truncated)

Commits

• 19b16bf release 0.21
• 45da7c2 document removal of Python 3.8 support and tagging of Python 3.13 support
• 2f3204a docmument new format='svg_inline' and add test coverage
• fb70498 bump version for switch to pyproject.toml and https://build.pypa.io
• bff786f Add svg_inline to formats.py
• 421925a update build instructions for https://build.pypa.io
• 77769e7 actually make lint-code.py respect pyroject.toml configuration
• 8a3a2b7 make lint-code.py respect pyroject.toml configuration
• ac77cf0 fix coverage section name
• 115ad34 replace setup.py, setup.cfg, and tox.ini with pyproject.toml
• Additional commits viewable in compare view

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