buildifier false pos on >>= operator

example code 
```
def foo(num):
    num >>= 4
    return num
```

result `no-effect: Expression result is not used. (https://github.com/bazelbuild/buildtools/blob/main/WARNINGS.md#no-effect)`

These operators do have an effect, and you can clearly see the number shifting if you print num before and after.

Tested with 8.0.2