Use fixed source code for parser context (#7717)
## Summary
The parser now uses the raw source code as global context and slices
into it to parse debug text. It turns out we were always passing in the
_old_ source code, so when code was fixed, we were making invalid
accesses. This PR modifies the call to use the _fixed_ source code,
which will always be consistent with the tokens.
Closes https://github.com/astral-sh/ruff/issues/7711.
## Test Plan
`cargo test`
