Ignore trailing quotes for unclosed l-brace errors

[charliermarsh]

Summary

Given:

F"{"ڤ

We try to locate the "unclosed left brace" error by subtracting the quote size from the lexer offset -- so we subtract 1 from the end of the source, which puts us in the middle of a Unicode character. I don't think we should try to adjust the offset in this way, since there can be content after the quote. For example, with the advent of PEP 701, this string could reasonably be fixed as:

F"{"ڤ"}"

Closes #9379.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.