Re-export importlib.metadata from _pytest.compat (#9906)

I'm fixing a bug in mypy's --no-implicit-reexport logic in
python/mypy#12704 and mypy-primer flagged this

Author: hauntsaninja

changelog/9906.trivial.rst

@@ -0,0 +1 @@
+Made ``_pytest.compat`` re-export ``importlib_metadata`` in the eyes of type checkers.

src/_pytest/compat.py

@@ -50,9 +50,11 @@ class NotSetType(enum.Enum):
 # fmt: on
 
 if sys.version_info >= (3, 8):
-    from importlib import metadata as importlib_metadata
+    import importlib.metadata
+
+    importlib_metadata = importlib.metadata
 else:
-    import importlib_metadata  # noqa: F401
+    import importlib_metadata as importlib_metadata  # noqa: F401
 
 
 def _format_args(func: Callable[..., Any]) -> str: