Fix quickstart command from requiring root positional argument (#3123)

Author: Tbruno25

docs/changelog/3084.bugfix.rst

@@ -0,0 +1 @@
+Fix ``quickstart`` command from requiring ``root`` positional argument

src/tox/session/cmd/quickstart.py

@@ -27,6 +27,7 @@ def tox_add_option(parser: ToxParser) -> None:
         "quickstart_root",
         metavar="root",
         default=Path().absolute(),
+        nargs="?",
         help="folder to create the tox.ini file",
         type=Path,
     )

tests/session/cmd/test_quickstart.py

@@ -53,3 +53,8 @@ def test_quickstart_refuse(tox_project: ToxProjectCreator) -> None:
 def test_quickstart_help(tox_project: ToxProjectCreator) -> None:
     outcome = tox_project({"tox.ini": ""}).run("q", "-h")
     outcome.assert_success()
+
+
+def test_quickstart_no_args(tox_project: ToxProjectCreator) -> None:
+    outcome = tox_project({}).run("q")
+    outcome.assert_success()