Use exceptiongroup for teardown errors

We might get exceptions from multiple steps of teardown, and now we have a way of reporting more than one!

src/_pytest/runner.py

@@ -15,6 +15,7 @@
 from typing import Union
 
 import attr
+from exceptiongroup import BaseExceptionGroup
 
 from .reports import BaseReport
 from .reports import CollectErrorRepr
@@ -512,22 +513,21 @@ def teardown_exact(self, nextitem: Optional[Item]) -> None:
         stack is torn down.
         """
         needed_collectors = nextitem and nextitem.listchain() or []
-        exc = None
+        exceptions = []
         while self.stack:
             if list(self.stack.keys()) == needed_collectors[: len(self.stack)]:
                 break
-            node, (finalizers, _) = self.stack.popitem()
+            _, (finalizers, _) = self.stack.popitem()
             while finalizers:
                 fin = finalizers.pop()
                 try:
                     fin()
                 except TEST_OUTCOME as e:
-                    # XXX Only first exception will be seen by user,
-                    #     ideally all should be reported.
-                    if exc is None:
-                        exc = e
-        if exc:
-            raise exc
+                    exceptions.append(e)
+        if len(exceptions) == 1:
+            raise exceptions[0]
+        elif exceptions:
+            raise BaseExceptionGroup("", exceptions)
         if nextitem is None:
             assert not self.stack