config: fix handling of venv opts env vars

This change correctly handles virtual environment creation options
provided via environment variables. For example, previously when
`POETRY_VIRTUALENVS_OPTIONS_SYSTEM_SITE_PACKAGES` was specified via an
environment variable, this was incorrectly ignored when a virtual
environment was created.

src/poetry/config/config.py

@@ -275,6 +275,11 @@ def get(self, setting_name: str, default: Any = None) -> Any:
 
             value = value[key]
 
+        if self._use_environment and isinstance(value, dict):
+            # this is a configuration table, it is likely that we missed env vars
+            # in order to capture them recurse, eg: virtualenvs.options
+            return {k: self.get(f"{setting_name}.{k}") for k in value}
+
         return self.process(value)
 
     def process(self, value: Any) -> Any:

tests/config/test_config.py

@@ -75,6 +75,23 @@ def test_config_get_from_environment_variable(
     assert config.get(name) is value
 
 
+def test_config_get_from_environment_variable_nested(
+    config: Config,
+    environ: Iterator[None],
+) -> None:
+    options = config.default_config["virtualenvs"]["options"]
+    expected = {}
+
+    for k, v in options.items():
+        if isinstance(v, bool):
+            expected[k] = not v
+            os.environ[f"POETRY_VIRTUALENVS_OPTIONS_{k.upper().replace('-', '_')}"] = (
+                "true" if expected[k] else "false"
+            )
+
+    assert config.get("virtualenvs.options") == expected
+
+
 @pytest.mark.parametrize(
     ("path_config", "expected"),
     [("~/.venvs", Path.home() / ".venvs"), ("venv", Path("venv"))],