Try disabling Poetry experimental installer

Author: thibaudcolas

tox.ini

@@ -19,6 +19,9 @@ deps =
 
 [testenv:lint]
 commands =
+    # For compatibility with Python 3.10.
+    # See https://github.com/python-poetry/poetry/issues/4210.
+    poetry config experimental.new-installer false
     poetry install -q
     poetry run flake8
     poetry run isort --check-only --diff

tox_install.sh

@@ -1,6 +1,9 @@
 #!/bin/sh
 set -e
 
+# For compatibility with Python 3.10.
+# See https://github.com/python-poetry/poetry/issues/4210.
+poetry config experimental.new-installer false
 poetry install
 
 if [ ! -z "$@" ]