F-string formatting: Invalid syntax for format-spec with double quotes when targeting pre Python 3.12

```py
f'{x:a{y=:{z:hy "user"}}} \'\'\''
```

Gets formatted to 

```py
f"{x:a{y=:{z:hy "user"}}} '''"
```

when preview mode is enabled and targeting a version < Python 3.12

This is related to https://github.com/astral-sh/ruff/pull/14493