test: fix test incorrectly checking for hash collision avoidance

tests/test_main.py

@@ -651,9 +651,11 @@ class TestModel(BaseModel):
     assert hash(m) == h
 
     # Keys can be missing, e.g. when using the deprecated copy method.
-    # This should change the hash, and more importantly hashing shouldn't raise a KeyError.
+    # This could change the hash, and more importantly hashing shouldn't raise a KeyError
+    # We don't assert here, because a hash collision is possible: the hash is not guaranteed to change
+    # However, hashing must not raise an exception, which simply calling hash() checks for
     del m.__dict__['a']
-    assert h != hash(m)
+    hash(m)
 
 
 def test_default_hash_function_overrides_default_hash_function():