Lexer start of line is false only for Mode::Expression (#8880)

## Summary

This PR fixes the bug in the lexer where the `Mode::Ipython` wasn't
being considered when initializing the soft keyword transformer which
wraps the lexer. This means that if the source code starts with either
`match` or `type` keyword, then the keywords were being considered as
name tokens instead. For example,

```python
match foo:
    case bar:
        pass
```

This would transform the `match` keyword into an identifier if the mode
is `Ipython`.

The fix is to reverse the condition in the soft keyword initializer so
that any new modes are by default considered as the lexer being at start
of line.

## Test Plan

Add a new test case for `Mode::Ipython` and verify the snapshot.

fixes: #8870

crates/ruff_python_parser/src/soft_keywords.rs

@@ -31,7 +31,7 @@ where
     pub fn new(lexer: I, mode: Mode) -> Self {
         Self {
             underlying: lexer.multipeek(), // spell-checker:ignore multipeek
-            start_of_line: matches!(mode, Mode::Module),
+            start_of_line: !matches!(mode, Mode::Expression),
         }
     }
 }