chore: update rexml to 3.3.9

[edisooon]

• [x] PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes: upgrade rexml to 3.3.9 to the Gemfile, and ran bundle update

How did you test these changes? (Please add a line here how the changes were tested)

Documentation update required?

• [x] No
• [ ] Yes (Please include a PR link for the documentation update)

General Checklist

• [ ] Added Unit Tests
• [ ] Added Integration Tests
• [x] Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.