Fix "make -C Documentation builder-image"

Use this workaround until the issue gets fixed:

yaml/pyyaml#601 (comment)

Signed-off-by: Michi Mutsuzaki <michi@isovalent.com>

Documentation/Dockerfile

@@ -22,7 +22,8 @@ RUN apk add --no-cache --virtual --update \
 
 FROM docs-base AS docs-builder
 ADD ./requirements.txt /tmp/requirements.txt
-RUN pip install -r /tmp/requirements.txt
+# Workaround for https://github.com/yaml/pyyaml/issues/601
+RUN pip install "Cython<3.0" pyyaml --no-build-isolation && pip install -r /tmp/requirements.txt
 
 ENV HOME=/tmp
 ENV READTHEDOCS_VERSION=$READTHEDOCS_VERSION