Strange warning in autosummary when literal block notation is used in first line of docstring

I noticed this warning when developing the docs in pyMOR. In the index.rst in pymor.algorithms/timestepping I get the warnings below. The warning originates in the docstring of the solve method.

/pymor/docs/source/autoapi/pymor/algorithms/timestepping/index.rst:71:<autosummary>:2: WARNING: Literal block expected; none found.
/pymor/docs/source/autoapi/pymor/algorithms/timestepping/index.rst:134:<autosummary>:2: WARNING: Literal block expected; none found.
/pymor/docs/source/autoapi/pymor/algorithms/timestepping/index.rst:191:<autosummary>:2: WARNING: Literal block expected; none found.

The problem is that autoapi tries to pick the first line of the docstring for the table and breaks if the first line of a valid docstring contains a literal block notation ::. This seems to be similar to an old issue in sphinx.

How to Reproduce

FROM python:3.9-slim

RUN apt update; apt install -y build-essential curl git unzip vim
RUN git clone https://github.com/pymor/pymor
WORKDIR /pymor
RUN pip install -e '.[full]'
RUN git fetch origin pull/1563/head:method-overview
RUN git checkout method-overview
RUN git revert --no-commit 3a4a17f13f206cac75d6fee30f76d2a0a57de46d..HEAD
RUN apt install -y python3-pyqt5
RUN sphinx-build -E docs/source docs/sphinx/

Your project

The docs in pyMOR.

OS

Linux

Python version

3.8, (3.7, 3.9)

Sphinx version

4.4.0

autoapi version

1.8.4

Reproduce the warning with the documented Docker setup and sphinx-build command, focusing on docs/source/autoapi/pymor/algorithms/timestepping/index.rst and the solve method docstring. Trace how autosummary selects the first docstring line when it contains ::; done means the documented build no longer emits the Literal block expected warning.