TracebackException.format_exception_only() mutates attributes on keyword typo suggestion

Bug description

TracebackException.format_exception_only() is not idempotent when _find_keyword_typos() finds a suggestion. The method directly mutates self.text, self.offset, self.end_offset, self.lineno, self.end_lineno, and self.msg, so a second call produces different output (e.g. wrong line number).

import traceback

code = "fr x in range(10):\n    pass\n"
try:
    compile(code, "<test>", "exec")
except SyntaxError as exc:
    te = traceback.TracebackException(type(exc), exc, None)
    r1 = list(te.format_exception_only())  # correct
    r2 = list(te.format_exception_only())  # different output
    assert r1 == r2  # fails

_find_keyword_typos was added in gh-132449.

CPython versions tested on

main

Operating systems tested on

macOS

Linked PRs

• gh-154545

從 traceback.TracebackException.format_exception_only() 和 issue 中描述的 _find_keyword_typos() 進入點開始。重現提供的 SyntaxError 範例，呼叫 format_exception_only() 兩次並比較結果。當重複呼叫產生完全相同的輸出（包括行號和其他例外詳細資訊）時，即視為完成。