chore: restrict virtualenv for Python 3.9 on Windows due to issues wi…

…th the embedded pip

pyproject.toml

@@ -70,9 +70,14 @@ shellingham = "^1.5"
 tomli = { version = "^2.0.1", python = "<3.11" }
 # exclude 0.11.2 and 0.11.3 due to https://github.com/sdispater/tomlkit/issues/225
 tomlkit = ">=0.11.1,<1.0.0,!=0.11.2,!=0.11.3"
+# trove-classifiers uses calver, so version is unclamped
 trove-classifiers = ">=2022.5.19"
 # exclude 20.4.5 - 20.4.6 due to https://github.com/pypa/pip/issues/9953
-virtualenv = "^20.4.3,!=20.4.5,!=20.4.6"
+virtualenv = [
+    { version = "^20.4.3,!=20.4.5,!=20.4.6" },
+    # see https://github.com/python-poetry/poetry/pull/6950 for details
+    { version = "<20.16.6", markers = "sys_platform == 'win32' and python_version == '3.9'" },
+]
 xattr = { version = "^0.10.0", markers = "sys_platform == 'darwin'" }
 urllib3 = "^1.26.0"