chore: clarify unknown-config breaking change note in changelog (#9733)

## What / Why

#9729 reverts the `.npmrc` file-config half of the breaking change from
`979518d` (#9276): unknown `.npmrc` configs warn by default again, and
the new `strict-npmrc` config opts back into erroring. Unknown CLI flags
and abbreviations still throw.

The `12.0.0-pre.1` changelog entry still carried the original wording,
which claimed unknown `.npmrc` configs now throw. Since release-please
aggregates every prerelease `BREAKING CHANGE` note into the eventual
stable `v12.0.0` release notes, that stale line would surface
(inaccurately) in the 12.0.0 notes. This corrects the wording in place.

## Change

Edits the single breaking-changes bullet in the `## [12.0.0-pre.1]`
section:

> unknown CLI flags, abbreviated flags, and single-hyphen multi-char
shorthands now throw instead of warning. (Unknown `.npmrc` configs still
warn by default; opt into erroring with the new `strict-npmrc` config.)

## Notes

- Manual, targeted edit to an already-released, release-please-generated
section — this does not disturb release-please, which derives versions
from git tags + commit history and only prepends new sections.
Precedent: #8298 (`chore: add contributor to changelog entry`).
- Best merged alongside / after #9729 so the corrected note reflects
shipped behavior.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>