Bump pygraphviz from 1.7 to 1.9 (#752)

Bumps [pygraphviz](https://github.com/pygraphviz/pygraphviz) from 1.7 to 1.9.
- [Release notes](https://github.com/pygraphviz/pygraphviz/releases)
- [Changelog](https://github.com/pygraphviz/pygraphviz/blob/main/RELEASE.rst)
- [Commits](pygraphviz/pygraphviz@pygraphviz-1.7...pygraphviz-1.9)

---
updated-dependencies:
- dependency-name: pygraphviz
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pyproject.toml

@@ -32,7 +32,7 @@ ffcx = "ffcx:__main__.main"
 [project.optional-dependencies]
 lint = ["ruff"]
 docs = ["sphinx", "sphinx_rtd_theme"]
-optional = ["numba", "pygraphviz==1.7"]
+optional = ["numba", "pygraphviz==1.9"]
 test = ["pytest >= 6.0", "sympy", "numba"]
 ci = [
     "coveralls",