Sphinx 3.2.0 breaks 'docs' build

[tseaver]

From this Kokoro build:

Traceback (most recent call last):
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/cmd/build.py", line 280, in build_main
    app.build(args.force_all, filenames)
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/application.py", line 348, in build
    self.builder.build_update()
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/builders/__init__.py", line 297, in build_update
    self.build(to_build,
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/builders/__init__.py", line 311, in build
    updated_docnames = set(self.read())
  File "/usr/local/lib/python3.8/contextlib.py", line 120, in __exit__
    next(self.gen)
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/util/logging.py", line 213, in pending_warnings
    memhandler.flushTo(logger)
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/util/logging.py", line 178, in flushTo
    logger.handle(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1587, in handle
    self.callHandlers(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1649, in callHandlers
    hdlr.handle(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 946, in handle
    rv = self.filter(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 807, in filter
    result = f.filter(record)
  File "/tmpfs/src/github/python-bigquery/.nox/docs/lib/python3.8/site-packages/sphinx/util/logging.py", line 421, in filter
    raise exc
sphinx.errors.SphinxWarning: /tmpfs/src/github/python-bigquery/google/cloud/bigquery/query.py:docstring of google.cloud.bigquery.query.ScalarQueryParameter:15:Field list ends without a blank line; unexpected unindent.

Warning, treated as error:
/tmpfs/src/github/python-bigquery/google/cloud/bigquery/query.py:docstring of google.cloud.bigquery.query.ScalarQueryParameter:15:Field list ends without a blank line; unexpected unindent.