update docs build

.github/workflows/deploy_docs.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/checkout@v2
       - name: Set up python
         id: setup-python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: '3.7'
       #----------------------------------------------
@@ -27,6 +27,11 @@ jobs:
       - name: Install Poetry
         uses: snok/install-poetry@v1
         with:
+          # Poetry seems to have dropped official support for Python 3.7
+          # but we need it for PyQt build artifacts. Pin poetry version.
+          # See https://github.com/snok/install-poetry/issues/131
+          # and https://github.com/python-poetry/poetry/pull/7674
+          version: 1.5.1
           virtualenvs-create: true
           virtualenvs-in-project: true
           installer-parallel: true