error: else prong required when switching on type 'void'

### Zig Version

0.16.0-dev.747+493ad58ff

### Steps to Reproduce and Observed Behavior

```zig
pub fn main() !void {
    switch({}) {
        {} => {},
    }
}
```

`zig run a.zig`

```
a.zig:2:5: error: else prong required when switching on type 'void'
    switch({}) {
    ^~~~~~
```

### Expected Behavior

There should be no error because all cases are handled