runner: avoid using node's store in SetupState

SetupState maintains its own state, so it can store the exception
itself, instead of using the node's store, which is better avoided when
possible.

This also reduces the lifetime of the reference-cycle-inducing exception
objects which is never a bad thing.

src/_pytest/runner.py

@@ -36,7 +36,6 @@
 from _pytest.outcomes import OutcomeException
 from _pytest.outcomes import Skipped
 from _pytest.outcomes import TEST_OUTCOME
-from _pytest.store import StoreKey
 
 if TYPE_CHECKING:
     from typing_extensions import Literal
@@ -467,29 +466,33 @@ class SetupState:
     """
 
     def __init__(self) -> None:
-        # Maps node -> the node's finalizers.
         # The stack is in the dict insertion order.
-        self.stack: Dict[Node, List[Callable[[], object]]] = {}
-
-    _prepare_exc_key = StoreKey[Union[OutcomeException, Exception]]()
+        self.stack: Dict[
+            Node,
+            Tuple[
+                # Node's finalizers.
+                List[Callable[[], object]],
+                # Node's exception, if its setup raised.
+                Optional[Union[OutcomeException, Exception]],
+            ],
+        ] = {}
 
     def prepare(self, item: Item) -> None:
         """Setup objects along the collector chain to the item."""
         # If a collector fails its setup, fail its entire subtree of items.
         # The setup is not retried for each item - the same exception is used.
-        for col in self.stack:
-            prepare_exc = col._store.get(self._prepare_exc_key, None)
+        for col, (finalizers, prepare_exc) in self.stack.items():
             if prepare_exc:
                 raise prepare_exc
 
         needed_collectors = item.listchain()
         for col in needed_collectors[len(self.stack) :]:
             assert col not in self.stack
-            self.stack[col] = [col.teardown]
+            self.stack[col] = ([col.teardown], None)
             try:
                 col.setup()
             except TEST_OUTCOME as e:
-                col._store[self._prepare_exc_key] = e
+                self.stack[col] = (self.stack[col][0], e)
                 raise e
 
     def addfinalizer(self, finalizer: Callable[[], object], node: Node) -> None:
@@ -500,7 +503,7 @@ def addfinalizer(self, finalizer: Callable[[], object], node: Node) -> None:
         assert node and not isinstance(node, tuple)
         assert callable(finalizer)
         assert node in self.stack, (node, self.stack)
-        self.stack[node].append(finalizer)
+        self.stack[node][0].append(finalizer)
 
     def teardown_exact(self, nextitem: Optional[Item]) -> None:
         """Teardown the current stack up until reaching nodes that nextitem
@@ -514,7 +517,7 @@ def teardown_exact(self, nextitem: Optional[Item]) -> None:
         while self.stack:
             if list(self.stack.keys()) == needed_collectors[: len(self.stack)]:
                 break
-            node, finalizers = self.stack.popitem()
+            node, (finalizers, prepare_exc) = self.stack.popitem()
             while finalizers:
                 fin = finalizers.pop()
                 try: