Fix missing leading space in suggestion
For a local pattern with no space between `let` and `(` e.g.:
```rust
let(_a) = 3;
```
we were previously suggesting this illegal code:
```rust
let_a = 3;
```
After this change the suggestion will instead be:
```rust
let _a = 3;
```
Fixes#117380
9e4ab9f111