gh-128481: indicate that the default value for `FrameSummary.end_lineno` changed in 3.13 (#130755)

The value taken by `FrameSummary.end_lineno` when passing `end_lineno=None` changed in gh-112097.

Previously, a `end_lineno` could be specified to be `None` directly but since 939fc6d, passing None makes
the constructor use the value of `lineno` instead.