Drop dependency on py.io

Pytest 7.2.0 dropped its dependency on the `py` package. We don't
specify `py` explicitly as a dependency, so tests starting failing since
the release of pytest 7.2.0.

To drop this dependency, pytest vendored `py.io.TerminalWriter` into
`_pytest._io` in pytest commit 276405a03 (6.0.0rc1). It looks like we
still support pytest 5.0 —at least it's listed in tox.ini— so I fall
back to importing from `py.io` if it isn't present in `_pytest`.

This was our only direct use of the `py` library.

src/pytest_bdd/generation.py

@@ -5,9 +5,13 @@ import itertools
 import os.path
 from typing import TYPE_CHECKING, cast
 
-import py
 from mako.lookup import TemplateLookup
 
+try:
+    from _pytest._io import TerminalWriter
+except ImportError:
+    from py.io import TerminalWriter
+
 from .feature import get_features
 from .scenario import inject_fixturedefs_for_step, make_python_docstring, make_python_name, make_string_literal
 from .steps import get_step_fixture_name
@@ -79,7 +83,7 @@ def show_missing_code(config: Config) -> int:
 
 def print_missing_code(scenarios: list[ScenarioTemplate], steps: list[Step]) -> None:
     """Print missing code with TerminalWriter."""
-    tw = py.io.TerminalWriter()
+    tw = TerminalWriter()
     scenario = step = None
 
     for scenario in scenarios:
@@ -166,7 +170,7 @@ def group_steps(steps: list[Step]) -> list[Step]:
 
 def _show_missing_code_main(config: Config, session: Session) -> None:
     """Preparing fixture duplicates for output."""
-    tw = py.io.TerminalWriter()
+    tw = TerminalWriter()
     session.perform_collect()
 
     fm = session._fixturemanager