Rename CODEOWNERS reviewer team: css-reviewers → engineer-reviewers (#682)

* Initial plan

* chore: replace @primer/css-reviewers with @primer/engineer-reviewers in CODEOWNERS

Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

Author: Copilot

.github/CODEOWNERS

@@ -1 +1 @@
-*       @primer/css-reviewers
+*       @primer/engineer-reviewers