6.18.0-beta1

What's Changed

• Allow configurable user attributes for Stepup by @pablothedude in #1828
• Update behat & remove abandoned container-interop/container-interop by @tvdijen in #1832
• Remove trailing slash on void elements by @tvdijen in #1837
• Fix bug: remember Choice cookie has double quotes around the entityID by @ArnoutvdKnaap in #1839
• Bump pbkdf2 from 3.1.2 to 3.1.3 in /theme by @dependabot[bot] in #1836

Full Changelog: 6.17.0-beta...6.18.0-beta1