Brace spacing when formatting f-strings is not idempotent

Formatting an f-string is not idempotent in Ruff 0.9.2 for an unparenthesized tuple whose first and only element starts with a brace.
```console
$ printf 'f"{ {}, }"\n' | ruff format --isolated -
f"{ ({},) }"

$ printf 'f"{ {}, }"\n' | ruff format --isolated - | ruff format --isolated -
f"{({},)}"
```