chore(validate-plugins,scan-plugins): re-pin to community 426e469f
Aligns all three shared community action pins on the same SHA (426e469f). The
validate-plugins/scan-plugins actions are unchanged between d207465 and 426e469f
(only bump-plugin-shas changed in #266/#267) — SHA-consistency, no behavior change.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>