Add precise values for enum members where possible (#11299)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Alex Waygood <alex.waygood@gmail.com>

stdlib/asyncio/locks.pyi

@@ -101,10 +101,10 @@ class BoundedSemaphore(Semaphore): ...
 
 if sys.version_info >= (3, 11):
     class _BarrierState(enum.Enum):  # undocumented
-        FILLING: str
-        DRAINING: str
-        RESETTING: str
-        BROKEN: str
+        FILLING = "filling"
+        DRAINING = "draining"
+        RESETTING = "resetting"
+        BROKEN = "broken"
 
     class Barrier(_LoopBoundMixin):
         def __init__(self, parties: int) -> None: ...