Bump rexml from 3.2.6 to 3.2.8

[github-actions]

Dependabot opened a pull request to update a dependency. Please review it: #410

• Comment on this issue tagging Chayn staff (@kyleecodes) to be assigned this issue.
• Follow directions in the Chayn Dependency Upgrade Guide here: https://chayn.notion.site/Chayn-Tech-Contributor-Wiki-5356c7118c134863a2e092e9df6cbc34?pvs=4