Prevented the pytest plugin from crashing on pytest < 7.0

Fixes #343.

docs/userguide.rst

@@ -148,8 +148,8 @@ functions with :data:`~typing.Any`.
 Using the pytest plugin
 -----------------------
 
-Typeguard comes with a pytest plugin that installs the import hook (explained in the
-previous section). To use it, run ``pytest`` with the appropriate
+Typeguard comes with a plugin for pytest (v7.0 or newer) that installs the import hook
+(explained in the previous section). To use it, run ``pytest`` with the appropriate
 ``--typeguard-packages`` option. For example, if you wanted to instrument the
 ``foo.bar`` and ``xyz`` packages for type checking, you can do the following:
 

docs/versionhistory.rst

@@ -11,6 +11,8 @@ This library adheres to
   (`#460 <https://github.com/agronholm/typeguard/issues/460>`_; PR by @JelleZijlstra)
 - Fixed test suite incompatibility with pytest 8.2
   (`#461 <https://github.com/agronholm/typeguard/issues/461>`_)
+- Fixed pytest plugin crashing on pytest version older than v7.0.0 (even if it's just
+  present) (`#343 <https://github.com/agronholm/typeguard/issues/343>`_)
 
 **4.2.1** (2023-03-24)
 

src/typeguard/_pytest_plugin.py

@@ -2,15 +2,16 @@
 
 import sys
 import warnings
-from typing import Any, Literal
-
-from pytest import Config, Parser
+from typing import TYPE_CHECKING, Any, Literal
 
 from typeguard._config import CollectionCheckStrategy, ForwardRefPolicy, global_config
 from typeguard._exceptions import InstrumentationWarning
 from typeguard._importhook import install_import_hook
 from typeguard._utils import qualified_name, resolve_reference
 
+if TYPE_CHECKING:
+    from pytest import Config, Parser
+
 
 def pytest_addoption(parser: Parser) -> None:
     def add_ini_option(