inlining of superfluous var

The inlining of `a` is not suggested:
```python
def prepend(a, x):
    a = "*" * x + a
    return a
```
However, when providing the type `str` the refactoring ***is*** suggested:
```python
def prepend(a:str, x):
    a = "*" * x + a
    return a
```
