chore: blacken docs/conf.py (via synth)

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Commits in this repo since last synth:

Log from Synthtool

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
On branch autosynth
nothing to commit, working tree clean
HEAD detached at FETCH_HEAD
nothing to commit, working tree clean
.coveragerc
.flake8
.github/CONTRIBUTING.md
.github/ISSUE_TEMPLATE/bug_report.md
.github/ISSUE_TEMPLATE/feature_request.md
.github/ISSUE_TEMPLATE/support_request.md
.github/PULL_REQUEST_TEMPLATE.md
.github/release-please.yml
.gitignore
.kokoro/build.sh
.kokoro/continuous/common.cfg
.kokoro/continuous/continuous.cfg
.kokoro/docs/common.cfg
.kokoro/docs/docs.cfg
.kokoro/presubmit/common.cfg
.kokoro/presubmit/presubmit.cfg
.kokoro/publish-docs.sh
.kokoro/release.sh
.kokoro/release/common.cfg
.kokoro/release/release.cfg
.kokoro/trampoline.sh
CODE_OF_CONDUCT.md
CONTRIBUTING.rst
LICENSE
MANIFEST.in
docs/_static/custom.css
docs/_templates/layout.html
docs/conf.py.j2
noxfile.py.j2
renovate.json
setup.cfg
synthtool > Wrote metadata to synth.metadata.