fully soundness -> full soundness

Author: mikeshardmind

docs/spec/narrowing.rst

@@ -284,7 +284,7 @@ or by making the class to be narrowed final to avoid such a situation.
 In practice, such correctness is not always neccessary, and may work against
 your needs. for example, if you trust that users implementing
 the Sequence Protocol are doing so in a way that is safe to iterate over,
-the following function can never be fully sound, but fully soundness is not necessarily
+the following function can never be fully sound, but full soundness is not necessarily
 easier or better for your use::
 
     def useful_unsoundness(s: Sequence[object]) -> TypeIs[Sequence[int]]: