peg poetry version to 1.7.1 in doc build

Author: bckohan

doc/.readthedocs.yaml

@@ -15,7 +15,7 @@ build:
     post_create_environment:
       # Install poetry
       # https://python-poetry.org/docs/#installing-manually
-      - pip install poetry
+      - pip install poetry==1.7.1  # 1.8 has a bug preventing this build from working
       # Tell poetry to not use a virtual environment
       - poetry config virtualenvs.create false
     post_install: