release: @formio/core@2.6.6

[johnformio]

Automated sync from formio/nirvana for @formio/core@2.6.6 (monorepo 90f9df78da).

After merging, an engineer will tag the release:

git fetch origin
git tag v2.6.6 origin/master
git push origin v2.6.6

Generated by gh-workflows/bin/sync-oss.mjs.