Address no-access pyrefly error (#37888)

Author: jrmccluskey

sdks/python/apache_beam/utils/windowed_value.py

@@ -380,7 +380,7 @@ def from_windowed_values(
 
 
 try:
-  WindowedValue.timestamp_object = None
+  setattr(WindowedValue, 'timestamp_object', None)
 except TypeError:
   # When we're compiled, we can't dynamically add attributes to
   # the cdef class, but in this case it's OK as it's already present

sdks/python/pyrefly.toml

@@ -57,5 +57,4 @@ bad-specialization = "ignore"
 bad-context-manager = "ignore"
 invalid-yield = "ignore"
 bad-argument-count = "ignore"
-bad-typed-dict-key = "ignore"
-no-access = "ignore"
+bad-typed-dict-key = "ignore"